| [ Total Views: 529 | Total Replies: 7 | Thread Id: 19102 ] |
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 fatboy
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| posted on February 16th, 2004 at 10:22 PM |
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Hypothetical Brake Q (Kombi)
I've heard you can put commodore breaks on a Kombi - does this mean there is the possibility of ABS ?
" Captain Picard, why are there no Indians on the Enterprise ? Don't you need IT Support ? "
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modulus
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| posted on February 16th, 2004 at 10:29 PM |
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Yes and no. Commodore rotors (and clones of these by companies like DBA) are often used in e.g. 4-wheel-disk conversions.
This, by itself, doesn't get you very far towards ABS. For ABS at the very least you need to measure the rotation speed of each wheel and compare
it to some (independent?) measure of vehicle speed, then limit braking to each wheel independently.
Yes, there is the *possibility* of ABS. No, I'm not going to do it. Of course, you could always design it, install it, test it and write an
article for
http://www.aussiekombicampers.com
hth
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555bug
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| posted on February 17th, 2004 at 02:04 AM |
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simply yes, this was covered in one of the very first zoom mags. It works out just like a brake swap + the ABS unit, control bax and the funky sloted
disks (behind the rotor) so the control unit can deternin if a wheel is locked up. Sounds like a fun project  |
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 vw54
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| posted on February 17th, 2004 at 08:37 AM |
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ABS would be nice to have on a 65 Beetle... then again the wiring would be a nightmare
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modulus
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| posted on February 17th, 2004 at 11:19 AM |
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| Quote: | Originally
posted by 555bug
... so the control unit can deternin if a wheel is locked up...
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What happens when, as is quite common on wet or gravelled surfaces, you've got all four locked up? Where does the reference vehicle speed come
from? The spare wheel?
?
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555bug
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| posted on February 17th, 2004 at 11:49 AM |
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to the best of my knowledge each whel is fitted with a disk with X nimber of slots cut into it. (very much like an optical hall effects distributor)
as such the ABS control unit does not need to know the vehicles speed all it needs to know is that if the wheels were turning and you just hit the
brakes and all of a sudden all four wheels have stopped then it will just reduce the breake fluid pressur until it get a signal from each corner
again. I will dig out the article to double check these statements but I am pretty sure that this is how it works. |
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Purple Martin
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| posted on February 17th, 2004 at 12:18 PM |
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So if I'm already stopped, and I put my foot on the brake, will it release the brake pressure until I start rolling? I think that's why
modulus wants some other reference speed.
1959 red & white Beetle
1975 Kombi camper
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fatboy
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| posted on February 17th, 2004 at 12:57 PM |
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If possible could you scan a copy of the article - I'd love to read it
cheers
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modulus
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| posted on February 17th, 2004 at 06:09 PM |
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The wheels can be skidding under braking without being locked up.
If my true road speed is 120 kph, and LF thinks it's doing 60 kph (skidding) and RF thinks it's doing 90 kph (skidding) and LR thinks
it's doing 100 kph (slightly skidding) and RR thinks it's doing 0 kph (locked) -- who to believe?
One of the reasons for my curiosity about this is that the first ABS released in Australia were dead dangerous on gravel roads; they'd keep
kicking back the brake until you speared off, as they would tolerate no skidding....
[Edited on 17-2-2004 by modulus]
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555bug
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| posted on February 17th, 2004 at 09:06 PM |
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OK I have just read the article and it appears I was incorrect in regards to a vehicle speed sensor input. In my defence however the article is from
the Feb/March edition 1997 Zoom. Anyway here is teh blurb:
A typical ABS unit is made up of a number of input sensors reading wheel speed, an Eletronic control unit (ECU) and a Hydraulic control unit (HCU).
The wheel speed sensors are usually inductive sensors, using a permanent magnet surrounding a wire coil. On four channel systems, sensors are used on
all wheels. Triggering the sensor is a toothed ring ( called a tone wheel) attached to the wheel hub. In some systems a G-sensor is used to measure
deceleration.
In the most sophisticated systems the ECU compares the wheel speeds of the two diagonally opposite wheels - say the front right and the rear left.
From this it works out a reference speed and then compares the speeds of the other wheels. When a wheel starts rotating a lot slower that the
reference speed (because it is starting to lock up) the HCU pulses the brake fluid pressure for that wheels circuit. This pulsing can vary in
frequency between 4-10 times a second.
so there you go do it and let us know how you went.
[Edited on 17-2-2004 by 555bug] |
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