Steering control system for trailers

A forward motion steering control system for steering trailer wheels of a trailer towed by a tow vehicle in a forward direction, said trailer and said tow vehicle forming a vehicle system, said control system comprising:

• (a) a means for monitoring steering angles d.sub.t of the trailer wheels,
• (b) a means for repeatedly calculating a desired reference state for the vehicle system using a reference state equation selected from the group of equations consisting of:
• x.sub.r =Ax.sub.r +B.sub.c d.sub.c +B.sub.t d.sub.t,m,
• x.sub.r =-A.sup.-1 (B.sub.c d.sub.c +B.sub.t d.sub.t,m), and
• x.sub.r =-A.sup.-1 (B.sub.c d.sub.c,f +B.sub.t d.sub.t,m),
• where x.sub.r defines a dynamic reference model and x.sub.r defines a steady state reference model, and where d.sub.t is the steering angle of the tow vehicle wheels, d.sub.t,m is a steering command based on the speed of the tow vehicle, B.sub.c is calculated based on the longitudinal distance from the tow vehicle center of gravity to the trailer coupling, the mass of the tow vehicle and the stiffness of the vehicle system state, A is calculated based on stiffness of the vehicle system state arising from the tire/road interface, B.sub.t is calculated based on the mass of the tow vehicle, the longitudinal distance from the tow vehicle center of gravity to the trailer coupling, and the longitudinal distance from the trailer center of gravity to the trailer coupling, and d.sub.c,f is a filtered d.sub.t using an appropriately selected filter,
• (c) a means for repeatedly calculating desired steering angles d.sub.t,command for the trailer wheels that will bring the vehicle system towards said desired reference state, the calculation of d.sub.t,command being based on the difference between the actual vehicle state and the desired reference state, and
• (d) a means for repeatedly adjusting the steering angles d.sub.t of the trailer wheels in response to d.sub.t,command to bring the vehicle system towards said desired reference state and to maintain the vehicle system approximately at the desired reference state;
• wherein (c) comprises a means for executing a major loop to calculate d.sub.t,M, a means for executing a minor loop to calculate d.sub.t,m, and a means for calculating d.sub.t,command from d.sub.t,M and d.sub.t,m ;
• wherein said major loop is a calculation of major loop steering command d.sub.t,M using the equation d.sub.t,M =-Gb.sub.t *P(x.sub.1 -x.sub.r) where g is a matrix of scaling functions, and P is chosen to satisfy the Lyapunov Equation;
• and
• wherein said minor loop is a calculation of minor loop steering command d.sub.t,m using the equation d.sub.t,m =f(u).theta., where f(u) is a vector value function of the tow vehicle speed u.