Wheels lock up during braking

(Tractor/semi-trailer vehicle)

Steering Axle Lock Up

If the wheels on the steering axle lock up, the vehicle will travel essentially in a straight path, stable but unsteerable, as illustrated in figure below. The driver immediately senses this condition and If necessary to change direction, the driver can modulate the brakes to allow the steering axle wheels to roll up and regain steerability.

Trailer wheels Lock Up

If the trailer wheels lock up, the trailer will usually begin to swing slowly outside of the vehicle path, as shown in the figure below. When this occurs the driver again has time to modulate the brakes to roll up the trailer wheels and bring the trailer back in line.

Drive Axle Wheels Lock Up

However, if the, the vehicle will usually begin to jackknife, as shown in the figure below. When this occurs the process quickly becomes irreversible and the driver is unable to react fast enough to prevent total loss of control. This is one problem the driver is not able to handle without assistance, so this problem has been given number one priority.

The major cause of braking instability will be eliminated by installing antilock control on only the drive axles of a tractor/semi-trailer vehicle. The driver can apply the brakes in the usual manner but now has the critical assistance necessary for keeping the vehicle under control during the stop.