>Terry,
>Not according to the service manual. It has to actually sense a
differential
>in wheel RPMs between front and rear, not rate of decel. What you describe
>sounds like a good theory, however, I can find no refrence to what you
>describe as self cycling or sensing decel in the service manual. Perhaps I
>have missed it? Please send the page #'s so I can catch up.
>RSRBOB
>
You're right--it's not in the service manual. I only found out this stuff
when I installed my incomplete HU when I got it back from England. In the
service manual, if you look at the block diagram, it shows a "return pump".
It's just a couple of circles without any mechanical detail as to how the
pump actually works--it really is quite complex. There is some text
somewhere that mentions that there are "check valves" that prevent brake
fluid from the master cylinder working its way back through the return pump
path into the solenoids and "spools".
When I got my HU back from England, the guy had left out one of these check
valves--I had direct access to the solenoids and spools "from the back
door", if you will. Just riding the bike at slow speeds, I would snap the
throttle closed (causing a sharp deceleration--maybe even the differential
that the manual talks about). Then, while coasting against the engine, I
would very gently pull the front brake lever--not enough to apply the
brakes, but enough to "feel" what's going on down there. The lever was
pulsing like mad--the electric motor was running. This is how I determined
what I wrote about--not by anything included in the shop manual. The manual
basically assumes that this has already taken place.
I gave my manual to Jim Guss when I sold the GTS, but I recall some of the
info about how the ABS Failsafe Relay and the computer work together. I
spent a lot of time going over the wiring diagrams and even messed around
with the relay itself. Basically, during normal braking (no ABS
activation), there is no power to the electric motor -or- to the solenoids.
One side of the electric motor is always grounded to the chassis of the
bike, through the wiring harness. Basically, if you apply 12V to one side
of the motor, the other side is already connected to the battery ground,
completing the circuit, and the motor runs.
The solenoids are connected differently. The solenoids get 12V from the ABS
Failsafe Relay, similar to the motor. The other connection of the solenoids
(the ground side) goes directly to the computer. One side of the solenoid
has power available and the computer directly controls the "ground" side of
the solenoid when the ABS needs to "dump" fluid pressure. Using a
transistor as a switch, you can either choose to "source" current at 12
volts to a load that is already grounded, or you can "sink" current to
ground from a load that is already connected to 12 volts. The latter is
actually a little easier to accomplish and that's what the GTS ABS solenoids
do. This is why they call it a "Failsafe Relay". If the Failsafe Relay
ceases to function, for whatever reason, no power is even available to the
solenoids to cause the system to "dump"--no matter what the computer does.
If I haven't thoroughly confused, irritated, or offended you, and you want
to chat some more about this, we can take it offline, unless if the list
likes all of this technical drivel. This whole process was quite an
education and I've always wanted to write it up, but I just haven't had
enough time. I really like the way that the electric motor runs the return
pumps and check valves, but we can save that for another day. Basically,
the manual tells you about 70% or so of what's going on and tells you
nothing about how the hardware actually does it, because you're not supposed
to go in there messing around anyway . . . .
Terry Baker
