Semi-truck Anti-jackknife System

A semi-truck is said to be jackknifing if the angle between its tractor 41 and its trailer 42 increases undesirably – the tractor has veered leftward and is drifting rightward (as in Fig B), or it has veered rightward and is drifting leftward.  The rig becomes an unsteerable, multimillion-dollar threat to itself and others.  Drivers instinctively steer in the direction of drift, which would realign the tractor with its trajectory, if the front wheels could roll freely while other wheels are braked.

We (David M Regen, Samuel M Regen, Ingrid L Regen) recently patented our Jackknife-Prevention System.  It is a set of sensors (lateral-acceleration sensor 15, steering-direction sensor 16) and effectors (front-wheel-brake disablers 18,19) which help restore alignment of a sideward-skidding (drifting) semi-truck tractor 41 with its trajectory 43.  The lateral-acceleration sensor could be a mercury-ball tilt sensor, the steering-direction sensor could be a steering-angle sensor with appropriate processor or a three-way switch without a processor, and the brake disablers could be electrically powered three-way solenoid valves or three-way ball-cock valves.  In essence the system disables both front brakes of a leftward-drifting tractor when it is steered leftward or of a rightward-drifting tractor when it is steered rightward.  This allows the front wheels to advance faster than other wheels, thereby aligning the tractor with its trajectory and making the rig again steerable.  These actions should occur only when the key is on and the brakes are applied, so the sensors should receive signal power from the brake-light circuit and should trigger a relay to pass power from the key-on circuit to the effectors.

The actions to restore alignment of a sideward-skidding trailer-hauling tractor with its trajectory will also help restore alignment of any sideward-skidding vehicle with its trajactory, thereby reversing spin-out of any vehicle, including a trailerless semi-truck tractor.  Semi-truck drivers fear spin-outs as much as jackknifes.

A tractor can become misaligned several ways.  For example, the driver might apply brakes when the tractor’s right wheels are on a slippery area (liquid or gravel) or vise versa.  The tractor will veer to the side with greater traction.  If it veers leftward (as in Fig B), it will drift or skid rightward, and vise versa.  Another jackknife cause is braking while turning -- for example, braking while changing lanes, braking while dodging an obstacle or braking while exiting the highway via an off-ramp.  The trailer's inertia pushes the tractor's rear in the direction of the trailer's trajectory 43.  This push, being off-center with respect to the tractor's footprint, constitutes a spinning force to exaggerate the tractor's yaw.  Front-wheel unbraking in response to appropriate steering of a sideward-drifting tractor will restore alignment regardless of cause.

We contend that our jackknife-prevention system is effective under circumstances where alternative systems might fail.  We hope to licence our invention to at least one established semi-truck manufacturer or air-brake manufacturer.  The patent can be seen at:  JACKKNIFE PREVENTION SYSTEM  

Below is how the Jackknife Prevention System can be  conveniently implemented:

Design and Manufacture of Anti-jackknife/Anti-spinout Module

The Anti-jackknife System disables a semi-truck’s front-wheel brakes when the tractor is skidding sideward and the front wheels are steered in the direction of skid, so as to restore alignment of the tractor with its trajectory when the front wheels roll freely.

We have designed a module (Fig 1, below) with the steering-direction sensor 20+30 and lateral-acceleration (tilt) sensor 11 both in a single module which surrounds the steering column 1 and is anchored to the firewall via a brace 42,43,44 on which a relay 60 is mounted.  It's prototype is illustrated below:

The steering direction sensor has a rotor 20 pressed to the steering column 1 and bearing a strong magnet in its top front edge, and a stator 30 surrounding these and bearing a steel ball in a tunnel just outside the magnet's course, the tunnel having left-side conductors and right-side conductors.  The steel ball following the magnet joins the left-side conductors with each other when steering is leftward or joins the right-side conductors with each other when steering is rightward.

The sensors are essentially robust three-way switches (left on, right on, mid-off) connected in a left-side series and a right-side series from the key-on circuit to a relay which activates front-wheel brake-disabling valves.  If the mercury ball moves left and the rotor's magnet pulls the stator's steel ball left, then volts and amps pass to the relay which sends power to both left and right brake-disabling valves 18,19.  If the mercury ball moves right and the rotor's magnet pulls the stator's steel ball right, then volts and amps pass to the relay which sends power to both left and right brake-disabling valves 18,19.  No other condition activates the brake-disabling valves.

For tractors with antilock brakes, it may be possible for their front ABS valves to double as anti-jackknife/anti-spinout brake-disabling valves 18,19.