Semi-truck anti-jack-knife proposal

  * Considering a semi truck’s design, one can predict that it will jack-knife with little provocation – a modest left-right imbalance of braking traction or forceful braking during an avoidance turn.  After witnessing a jack-knifing incident up close, metal fragments dropping in my path, I have been imagining how such events can be prevented.  During a jack-knifing, the tractor points so much left or right, that steering is impossible.  Needed is a means to point the tractor in the direction of its motion, so the driver can steer it.
  *  I began by considering the range of tractor-to-trailer angles and front-wheel steering angles under common conditions.
  * Fig. 1 shows the angles during constant left turn.  The outer circle is the path taken by the tractor’s front mid-axle, the slightly smaller circle is the path taken by the tractor’s rear mid-axle, the inner circle is the path taken by the trailer’s rear mid-axle after it moves elliptically to its steady-state position.  In this illustration, the trailer’s axle-axle length (2 to 3) is thrice the tractor’s axle-axle length (1 to 2).  Once a steady state is established, a modest front-wheel pitch (1 in 3) will result in a substantial tractor-to-trailer pitch (~ 4 in 3).  

These paths might be followed during a U turn in a large lot, but typically the driver would cease turning before a steady state is established as illustrated in Fig 2, where the turn ends with a brief turn of the steering wheel in the opposite direction.

  * Here the driver takes the tractor on a wide sweep.  Approaching the side street, he/she will swing as far rightward as permitted, so the trailer’s rear wheels can best avoid a car in the left street’s oncoming lane.  For the same reason, he/she will pull as far beyond the intersection as permitted.  Early in the turn and until the tractor is in the side street, the tractor-to-trailer angel may be 90deg or slightly sharper.  Once the tractor's front wheels are in the eventual path, they will be steered rightward until the tractor's rear wheels are tracking in line.
  * Thus the relation between tractor front-wheel steering angle and tractor-to-trailer angle varies greatly during normal operation.  An algorithm and mechanism to prevent jack-knifing must freely allow those angles but quickly stop an increase of a tractor-to-trailer angle contrary to steering direction and/or it must rapidly halt and diminish a tractor-to-trailer jack-knifing angle.  A leftward jack-knife would be recognized as leftward tractor-to-trailer angle associated either with rightward drift of the tractor's rear wheels and/or with righward steering of the front wheels while skidding.  These conditions could be recognized by an optical device (analogous to an optical computer mouse) interacting with the road below the tractor's rear axle, perhaps aided by an accelerometer at this location.
  *  Figs 3 - 5 show a mechanisms to bring about the tractor-to-trailer angle responses.  
  *  In Figs 3 & 4, the mechanism consists of a servo-motor-driven spool (red) attached to the tractor's frame behind or below the cab, this connected by a cable or chain (green) to a large grooved hoop (red) attached to the trailer's frame concentric with the hitch.
  *  In Fig 3 the cable or chain crosses between the spool and grooved hoop.  The cable or chain wraps several times around the spool and is attached at its mid point.

  *  In Fig 4 a chain spans from spool to hoop on either side.  It doesn't wind on the spool, but engages a sprocket on the spool like a bicycle chain.

  *  In Fig 5, a servo-driven cog-wheel engages a larger ring attached reversibly to the trailer.

With sufficient strength of the elements, such a device should be able to halt and diminish a dangerous tractor-to-trailer angle move the angle toward optimal.