SierraNevadaAirstreams.org - Enjoyment of the whispering winds, the zephyrs, the airstreams of the Sierra Nevada and Great Basin areas of the United States.

Owners GuideUnderstanding -

Understanding brake controllers

In many places, towed vehicles (trailers) which weigh more than a ton or so are required to have their own brakes. Having brakes on the trailer means that they can stop faster with less stress on the tow vehicle brakes. Trailer brakes can also be a means to control sway or other instabilities.

Why trailer brakes?

Most states require that trailers that weigh several thousand pounds have their own braking system. This is primarily to assure quick and safe stopping, especially in panic situations. Stopping distance is only one of several advantages.

Without trailer brakes, stopping the trailer will push the vehicle forward and try to move the tow vehicle out of its way. This can create handling problems.

Using tow vehicle brakes to stop both the tow vehicle and the trailer can put significant stresses on the brakes increasing the chance of failure and wear.

Down hill braking can create a lot of heat in brakes. Good trailer brakes help keep tow vehicle brakes from getting too hot.

Sensing and acting

The first issue is how to tell your vehicle you want the brakes applied. You usually have two methods. One is the parking brake and the other is the brake pedal. Parking brakes are not usually applied when the vehicle is in motion and travel trailers usually do not have parking brakes (this is why wheel chocks are important trailer accessories).

When you press on the brake pedal, most vehicles use that motion to put pressure on a hydraulic cylinder that then pressurizes similar cylinders on each wheel's braking system. Back in the fifties, trailers used to use hydraulic brakes and the connection was a tap to the tow vehicle brake hydraulic lines. This has been phased out for safety and convenience reasons.

Modern brake controllers separate the tow vehicle and trailer brakes. The sense and measure tow vehicle braking and then send an electrical signal back to the trailer brakes to activate them. In the seventies, these brake controllers tapped into the tow vehicle brake hydraulic lines but, again, these have been phased out due to safety reasons and due to the complexity of modern ABS systems. Other methods need to be used to sense the demand for brakes to to create an action the trailer brakes can interpret.

from the vehicle motion

When you apply the tow vehicle brakes, it is going to slow down even with a trailer on behind. There are two ways to sense this motion. One is to use an accelerometer like a bob on a string and the other is to detect stress on the hitch.

U-Haul often uses surge brakes on its rental trailers. This is a mechanism on the hitch that activates the brakes as the tow vehicle pushes back on the trailer.



from the brake pedal position

from the hydraulic pressure









Resources






Support our site, Donations accepted thanks to the Amazon.com


TechComm Labs (tm)
copyright 2004 Leipper Management Group. All rights reserved Please address comments or questions to webmaster@leipper.org Last updated 11/01/2004
supporting and using open software
Sierra Nevada Airstreams - photograph policy -


note: all photographs on this site are for personal, private, and non-commercial use only. All other copyrights are retained by the individual photographers. See our policy. Disclaimer: any advice or suggestion presented is provided for informational purposes only and is correct and accurate only to the best of our knowledge at the time it was written. Anyone using such information does so at their own risk. Errors or omissions may exist and additional sources of information or appropriately licensed or qualified personnel should be consulted in deciding a course of action. We assume no liability or obligation by providing this information and warn any users of this information that they do so at their own risk. All links or references to commercial vendors or other sources of information and equipment do not intend or imply or convey any endorsement of that source or the product. They are provided strictly for informational purposes to illustrate the topic at hand. Sierra Nevada Airstreams Enjoyment of the whispering winds, the zephyrs, the airstreams of the Sierra Nevada and Great Basin areas of the United States is a personal, nonprofit, noncommercial web site intended for educational and recreational use only. This site is supported by volunteer effort and contributions.