Electric Trailer Brakes, (Revisited)

wrote:
It makes me wonder if you
could design a simple controller which could detect swaying and selectively
apply the brakes to counter it, either automatically or with driver
intervention.


Already done.
Some trailer brake controllers offer this, and has been offered as far
back as the early 1980's, or earlier. Some of the new factory
installed trailer packages are including this feature on new vehicles
destined to be tow vehicles.

On Jun 6, 2:10 pm, wrote:
In fact, I
would think that if you hit the trailer brakes that if anything it would make
the trailer more likely to sway. Afterall, when you want to drift a car,
the easiest way to do that is to pull the emergency brake. It transfers weight
forward and off the rear wheels (on in this case the trailer wheels) and it
reduces the available traction for the tires to counter the swaying.
Admittedly, removing weight from the back end reduces the polar moment as
well.
At one time I drove semi's and they have two ways to apply brakes; one
(a pedal) worked exactly like your car (operated all the brakes) the
other was a lever in the cab to operate the trailer brakes only. The
rig could be slowed down or stopped using the trailer brakes only,
theoretically a sure way to prevent jackknifing. I can tell you that
tapping that trailer brake took the sway out very nicely. While it
worked very well, owner/operators were rumored to use only the trailer
brakes to save on their tractor brakes. This would cause premature
brake failure of the trailer brakes and that would lead to some
interesting situations during panic stops or runaway conditions with
very effective tractor brakes and no brakes on the trailer.

Anyway, I think maybe you are not understanding the use of the E brake
in a drifted turn, which is done to break traction on the wheels
(inducing drift) and not primarily for weight shifting (I think).

Controlling sway with that lever in the cab of a semi (it's called a
trolley bar BTW) works only if the rear duals have some level of
adhesion, in which case you didn't need to use it in the first place.
If the trailer duals are already loose (or on the edge), really bad
things can happen when you yank the trolley bar. I suspect the effect
is similar with an electric brake controller.

Most owner-operators have compression (Jake) brakes fitted to the
engine and use the air brakes mostly to hold the rig in place at
stoplights and the like, the exception being panic stops where you
need all the help you can get. No need for brake-saving strategies if
you don't use them much in the first place. It's very much like a
spot landing, you want to run out of enery right at the stopping
point.

The above suggests a good strategy for towing any trailer - think far
enough ahead of the combination that you can do much of your slowing
with engine braking, keep the rig rolling slowly when approaching a
stop-light (stopping and restarting costs fuel and adds wear and tear)
and, as much as possible, use the brakes only to hold the vehicle in
place when stopped. Change lanes to permit vehicles entering an
interstate to merge. In this way, you won't be forced to slow down
and if they do something stupid ( I once saw a four-wheeler stop and
back up), you're already by them. Amuse yourself by trying to predict
what the drivers around you are likely to do next. With practice you
can get surprisingly good at it.

Ray Warshaw
1LK





there was the least bit On Jun 9, 12:20*pm, brianDG303
wrote:
On Jun 6, 2:10 pm, wrote:
* In fact, I would think that if you hit the trailer brakes that if anything it would make
the trailer more likely to sway. *Afterall, when you want to drift a car,
the easiest way to do that is to pull the emergency brake. *It transfers weight
forward and off the rear wheels (on in this case the trailer wheels) and it
reduces the available traction for the tires to counter the swaying.
Admittedly, removing weight from the back end reduces the polar moment as
well.

At one time I drove semi's and they have two ways to apply brakes; one
(a pedal) worked exactly like your car (operated all the brakes) the
other was a lever in the cab to operate the trailer brakes only. The
rig could be slowed down or stopped using the trailer brakes only,
theoretically a sure way to prevent jackknifing. I can tell you that
tapping that trailer brake took the sway out very nicely. While it
worked very well, owner/operators were rumored to use only the trailer
brakes to save on their tractor brakes. This would cause premature
brake failure of the trailer brakes and that would lead to some
interesting situations during panic stops or runaway conditions with
very effective tractor brakes and no brakes on the trailer.

Anyway, I think maybe you are not understanding the use of the E brake
in a drifted turn, which is done to break traction on the wheels
(inducing drift) and not primarily for weight shifting (I think).