Tractor-Trailer Jackknife Prevention Device

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INTERSTATE CLOSED AGAIN DUE TO JACKKNIFED TRACTOR TRAILER! This headline occurs far too frequently. Truck jackknives occur when the deviation angle between the tractor and the trailer gets too large. The front of the tractor moves like the folding blade of a jackknife (See Figure 1).

I am proposing (1) a sensing system (based upon accelerometers sensing relative motion between the front and back of the cab) and (2) a mitigation system that uses controlled bursts of horizontally directed gas pressure to counteract the motion before it becomes critical.

There are already several anti-jackknifing patents, but they are usually for devices to inhibit rotation of the “fifth wheel” (the connection between the tractor and the trailer) beyond some limit. Therefore, they only come into play when the vehicle is at the threshold of jackknifing, and are not dynamically related to the vehicle motion.

Another type of patent is for an automated or manual modification of the braking system, with differential braking force applied to effectively “steer” by braking. However, many jackknifing incidents occur when the road is slippery, and conventional braking is ineffective.

So what would be a better system? It would incorporate two parts: (1) a sensing subsystem (to determine when there is a potential for jackknifing), and (2) a mitigation system (to act in a way that will decrease the potential for jackknifing).

Trucks nowadays are replete with computer-aided sensors. Only two additional sensors would be needed: accelerometers at the front and at the rear of the tractor (Figure 2). Both of the accelerometers would measure acceleration in the horizontal plane, and in a direction perpendicular to the normal direction of travel. Relative motion (acceleration and integrated velocity and displacement) of the front and rear of the tractor would be continuously monitored to determine when relative trajectories indicate that jackknifing may develop.

When the processing microcontroller detects this condition, mitigation would be achieved by application of a burst or bursts of gas pressure, much in the manner of a thrust-reverser on a jet engine. In this way, no reliance is made on road surface conditions. The sensors would continue to monitor relative motion of the front and the rear of the tractor. If there were an overshoot, a gas pulse could be produced in the opposite direction.

Several methods of generating a gas pulse are possible. A few examples are (in order of decreasing effect): (1) a dedicated gas production from detonation of a stored fuel source; (2) using compressed air from the braking system; (3) using the exhaust of the engine forced through a nozzle.

Naturally, the system must be tested to determine levels of relative motion and trajectories that are indicative of jackknife potential. Furthermore, the mitigating gas pulse must be directed so that it does not adversely affect neighboring vehicles. Given these constraints, though, this system has the potential to significantly decrease the occurrence of accidents due to jackknifing.


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  • Name:
    Doug Anderson
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  • Software used for this entry:
    Microsoft Word; Adobe Photoshop Elements 3
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