ABS vs. FAS
 

Ever have one of those late night moments where you wake up with a start and realize something important?

I was thinking about the brake thread from yesterday and I found myself wondering if anyone has tried the ABS system during an FAS. I haven't had a chance to try it yet. I called Honda this morning about it and they were not helpful.

My concern is if there enough stored pressure to allow the ABS to operate to a complete stop from freeway speeds without draining all the pressure. If the ABS rapidly drains the pressure (as I suspect) then it transforms from a safety-enhancing device into a device that guarantees you will be relying on the mechanical brake backup in a panic stop when the motor is off.

I read a lot of ABS technical articles on the web this morning but was unable to find a definitive answer to the question. I could determine that ABS systems generally work by draining pressure in spurts, simulating pumping the brake but able to do it for each tire individually. Unfortunately pumping the brake pedal is the worst possible thing you can do when trying to come to a stop relying on stored pressure.

Some of the ABS systems I read about use an electric motor to maintain brake pressure (a good thing that could avoid this potential problem), but the HCH clearly does not maintain brake pressure with the ICE off.
I apologize for bringing this up again, but lives (or hopefully just insurance premiums) are at stake so please bear with me. Once the problem is fully understood then I will happily let it rest.

thanks,
Kurt

Re: ABS vs. FAS
 

Lakedude had a first hand experience with that situation.

Look here:

https://www.greenhybrid.com/discuss/...ead.php?t=2954

Re: ABS vs. FAS
 

Excellent! That answers the question from 20 mph, and confirms that ABS kicks in when the ICE is off, but does not answer the question if there is enough stored pressure to ride the ABS down to a stop from 60 mph.

It sounds encouraging however.

Re: ABS vs. FAS
 

My 05 Accord does well in panic stop with FAS. And had plenty of vacume to get the job done. Also tested with no vacume assist and it all worked out fine. There is alittle bit of resetance when the pedal is first massed on then it goes right on down and brakes hard.Tested it on old hwy 75. But if you use the brakes lightly as I did this morning coasting up to traffic compressing at a light in FAS I did run out of vacume assist. Its wasnt a problem for me.

Men,, be men and press on that brake pedal dont whussy out! If you cant stop a Civic without power brakes and drive thru a problem. You may need to go see a doctor... :)lmao

Re: ABS vs. FAS
 

Hi Psyshack:

___You definitely have a way of saying things the way you see them … I was LMAO on that one :D

___Good Luck

___Wayne R. Gerdes
___Waynegerdes@earthlink.net

Re: ABS vs. FAS
 

You guys must live in some flat areas, there are some hills where I live that you cannot slow down the car without assist. On my road bike (not motorcycle, the kind you pedal) I can get up to 55mph with the help of gravity alone. Try doing an FAS and then a panic stop in that situation. ;)

Re: ABS vs. FAS
 

Hi Livvie:

___Because of fuel cut during regen, if you can maintain your speed because of a relatively steep slope, there should be no reason for a FAS. I would never FAS down a slope where I would be accelerating well above the limits while coasting w/ ICE off. In my own area (flatlands of Illinois) FAS’ always comes about w/ a gradual bleed off of speed except for the rare D-FAS’ when they are available and I am always bleeding off speed very quickly because of an incline after the decline running through the bowl.

___All said and done, you do not just perform a FAS anywhere. Caution before action is always the best policy.

___Good Luck

___Wayne R. Gerdes
___Waynegerdes@earthlink.net

Re: ABS vs. FAS
 

Somehow this whole topic reminds me of a thread over at Edmunds.
I mentioned that in some instances, on vacant roads, in the middle of the night, on a gently graded downhill I'll switch it to N and just roll, letting it idle.
(Didn't even bring up FAS)

Wow! What a mistake that was.
Even a moderator jumped in and compared it to an experience he had when he rode his brakes all the way down a steep mountainside. When he was suprised by an unexpected light on the bottom and it was red, he "Careened through the red light uncontrolled because of his overheatd brakes" then said "Hey, it's your life not mine"

It was the last time I ever posted FE tips there.

Which brake pressure are you referring to?
Yes, the brake vaccume assist is limited but the important hydraulic (Which acutally stops the car) remains uneffected.

Re: ABS vs. FAS
 

Wayne, that makes sense.

My point is that braking a civic without assist in many cases is beyond the average person's strength. This applies mainly to those doing FAS. I agree that an FAS should only be done in places where it is "safe". But commons sense seems to be missing in a lot of people these days.

Re: ABS vs. FAS
 

I've only had the ABS kick in one time during a FAS so please keep in mind the sample size before making you own choices. I have run the vacuum assist out a few times and nearly put my car thru the back of the garage. I've been learning how much assist the vacuum can put out before running out, in fact last night I rode the brakes for a long while without running out of assist. I'm still not exactly sure what depletes the vacuum and what does not but it seems like you run out quick if you make brake applications and let off each time. Riding the brake in the same spot without letting off does not seem to use much vacuum.

BTW I don't know how the ABS would work if you had run out of vacuum. Also all this info only applies to my car which is a 2005 HCH. I assume the other Civics would be similar. I think doing a FAS on a older car with a vacuum leak would be dangerous.

Re: ABS vs. FAS
 

Hi Livvie:

___We have found common ground :D

___When I ran out of vacuum assist in the Insight, she was definitely what I would call in a "very slow" coast and my hands were on the emergency. If I found myself at 30 + without assist in traffic, I would consider a re-start and shutdown to rebuild vacuum but it would really be dependant on the surrounding traffic as in “if there was any”?

PS: I still owe you and Tbaleno a test segment between FAS and a neutral - idle - coast. I will get to it sooner or later …

___Hot_Gerogia_2004, I remember many of those threads over at Edmunds and they got so out of control so fast :( I truly believe the majority here push tanks so you have a captive but still questioning audience. The questioning of both the Pro’s and the Con’s are just as important but over there, you had just about any goof ball that could type on a computer, let alone those that could give a **** about why we all push tanks in hybrids and non-hybrids in the first place … I am exaggerating but this thread is relatively balanced vs. just about any thread over at Edmunds imho. I am just as guilty on the other side of those arguments in some cases so I can definitely sympathize with you in regards to the attacks. I was and still am hesitant to bring up some of our more “advanced” techniques up over at DriveAccord.net as well but Psyshack jumps in with both feet and takes the reigns there when needed as of late ;)

___Lakedude, that was a very important post. I think I will find the limits of my Accord’s vacuum assist on my next commute as it is definitely a consideration and knowledge as to when it runs out could be a life saver.

___Good Luck

___Wayne R. Gerdes
___Waynegerdes@earthlink.net

Re: ABS vs. FAS
 

Ok check this out:

http://auto.howstuffworks.com/power-brake2.htm

Look at the recharge operation when the red comes back in. This confirms my observations. Pumping the brakes is gonna deplete the vacuum reserve. Steady pressure will make the vacuum last longer.

Re: ABS vs. FAS
 

But does the abs pumping count as pumping? Or does it use some other system?

Re: ABS vs. FAS
 

http://auto.howstuffworks.com/anti-lock-brake1.htm

See Pump.

Re: ABS vs. FAS
 

I still don't follow. It sounds like the pump creates the vacum and doesn't take it from the master cylinder.

Re: ABS vs. FAS
 

I'm no expert having just learned this stuff today.

What I get out of it is that the big canister provides power assist so long as there is vacuum. If vacuum runs out you must provide the power with your foot and leverage like a non power system.

The ABS is a completely seperate system that is powered electrically which has a hydraulic pump that has nothing to due with the vacuum canister. It is the ABS that might let pressure off of a wheel so it is the ABS that puts the pressure back once the wheel is no longer locked up. It does this independant of your foot and the vacuum can.

Re: ABS vs. FAS
 

I'm thinking you will be restarting your car after an ABS incident anyway.

Re: ABS vs. FAS
 

Lakedude, as far as I am aware ABS does not work once the motor is off. Am I missing something here?

Re: ABS vs. FAS
 

Yes you still are. As I've mentioned several times already ABS does work during a FAS. At least it did the one time I had to stop for tree in the road.

Re: ABS vs. FAS
 

So then you could find yourself in a situation where you have no vacuum assist but you manage to somehow press the brake pedal to the point that a lockup would occur, and the ABS system kicks in? That's pretty **** funny.

Re: ABS vs. FAS
 

I'm not sure about that one because it has never happened but yes what you said does seem to be the case. I'll try it later.

Re: ABS vs. FAS, thanks and summary so far
 

This thread has been really helpful, thanks folks. I am really glad I made the switch from edmunds to this forum.

Here is a summary of what I have come away with: :lightbulb

I was confused and thought that assist pressure and brake pressure were the same thing.

Either the assist or the mechanical backup can produce brake pressure to the calipers.

ABS bleeds brake pressure from the calipers not the assist. The ABS pump cannot repressurize the assist either, as it can only restore fluid/pressure lost during the ABS process. Therefore it does act to preserve whatever level of assist you have because it keeps you from having to further depress the pedal to restore brake fluid drained off by the ABS system. Another way of describing it is that ABS is a circulatory system, it bleeds pressure from the calipers and then pumps it right back into the master cylinder, thus keeping the main brake pressure constant.

My misconception was I thought the assist pump was used to restore fluid drained by the ABS, I did not know about the electric pump that is part of all ABS systems.

Other people who have observed that the act of depressing the pedal (as opposed to holding it) is what loses assist pressure are right on.

Therefore one can use ABS with or without assist pressure. The ABS warning light does not come on during an FAS either, so it thinks it is ok too. Thus depressing and holding the brake pedal during an FAS (even to the point of activating ABS) is an efficient and safe use of pressure, unlike pumping.

Here is a choice quote from an ABS article:

"ABS can only reduce pressure, therefore brake pressure can never be more than what the brake pedal allows".

I for one am not strong enough to activate the ABS without assist (unlike psyshakennegger, whom I respect and admire but don't have his leg strength, although I reject insinuations impugning my masculinity :-) ).

So I will now happily FAS, even at freeway speeds, but be careful to keep my brake pressure up by starting the engine anytime I release (not depress) the brake pedal.

Note: In case it is not clear, yes ABS will function with or without assist pressure if I understand things correctly and your leg is strong enough. I am looking forward to lakedude trying it.

Re: ABS vs. FAS
 

Kurt, you and I agree about how all this brake stuff works. I pumped the brakes till the vacuum assist was gone and then tried to slam on the brakes hard enough to kick on the ABS but I didn't have the legs for it either. Last night I tried the Vette, I might try again in the Civic using both feet. Stopping cars without assist is not fun.

Re: ABS vs. FAS
 

That's what I thought, it will be too hard to engage the ABS if all assist is gone. The only way it will come on is if the surface is slippery... like loose dirt on pavement or snow.

Re: ABS vs. FAS
 

I can't imagine too many instances where people will be using a fas and riding the brake and then need to slam the brakes for an emergency. I guess the key is that if you bleeding the brakes by pumping them you should probably restart the car to get the resevoir filled.

Re: ABS vs. FAS
 

....and keep foot #2 ready.
I hope nobody's doing this in heavy traffic or high speed.
Safety #1 :thumbs_up

Re: ABS vs. FAS
 

And as Tom indicated, perhaps your Right Hand on the emergency brake lever to activate your rear brake(s). I assume the emergency brake actuates both rear brakes.

This has been an interesting thread. I think it would be cool if Honda put a button on your steering wheel that would engage a FAS. It would "kill" the engine, but then bring you right back to II on your ignition. Then whenever you hit the brake pedal, the computer would somehow disengage your CVT, restart the engine, reengage the CVT, and you'd be back to normal. Sort of a reverse of what happens during an auto stop where releasing the brake pedal starts the engine.

I can visualize this process in my mind, and I'm sure it could be designed. I suppose it could be set up to happen automatically whenever you take your foot off the accelerator for more than say 5 seconds. The car would put itself into FAS, and then reengage ICE if you hit the brakes while traveling at speed.

Does this make sense? :confused:

Mike

Re: ABS vs. FAS
 

yeup... all the systems are there... take the cruise control option and reverse it, brake is pressed, cruise control goes off... so there are system that go off when an brake event occurs. in this case we want to start the car. and since cruise only works at above 25mph (i don't know the exact number) you could use the same limit.

Re: ABS vs. FAS
 

I posted this bit in a thread about reboots a while back, but I thought it might be worth bringing up again...

:lightbulb HCH CVT Semi-forced autostop:

My understanding of the 2004 HCH is that the computer has a few things it looks for before it will perform an autostop. Engine temp has to be in the normal range, there has to be adequate vacuum pressure, IMA battery levels, the mph of the car has to rise past 10 mph and then fall below it again (for the CVT), and the brake has to be depressed (for the CVT). (there may also be an angle sensor involved as well, but I haven't experienced it enough to be certain)

My idea for a semi-forced autostop for the CVT HCH:
two switches
one momentary, the other a toggle with an annoying blinking led.

The toggle switch would be connected to the same wires as the brake light switch on the pedal, making the computer think I'm riding the brake but without putting any pressure or depleting vacuum. The annoying blinking led would remind me that it was on because my brake lamps will remain lit during this CVT forced autostop.

The momentary switch would be connected to the tach from the wheels and would serve as a momentary disconnect causing the computer to think that the car is moving slower than 10 mph for a brief moment.

By flipping the brake switch on and then hitting the tach momentary switch, I think it would satisfy the computer's requirements for an autostop.

This would seem to give me full control of the CVT HCH, the 12v would still be connected to the 144v IMA, and I'd have the ability to come out of autostop in an emergency by pressing the brake or by pressing on the gas like normal. When I'm done with the semi-forced autostop, I flip the brake switch to off and it takes the car back out of autostop. (The annoying blinking LED is to remind me that my brake lights are on in case I come out of autostop by any other means)

Any other thoughts or parts I missed?

Also, has anyone with a CVT HCH been in an actual autostop (not FAS) and coasted down a large enough hill to reach higher speeds (40+) and before coming out of it? How do the engine and transmission react?