Computer controlled steering system for vehicles having two independently driven wheels

A computer controlled steering system for vehicles utilising two independent drive wheels can be used to improve the ability of such vehicles to resist external side forces, such as that which occur when traversing steep slopes. The objective is achieved by using an onboard computer, utilising a specially-developed software algorithm, to positively control the steer angles of the non-driven wheels (usually these are castors). The software algorithm uses the mathematical relationship between the drive wheel speeds and the steer angles of the non-driven wheels. The algorithm ensures that the turning radius produced by the drive wheel speeds is the same as that produced by the steer angles. The vehicle motion includes conventional turning but also rotation about the centre of the drive axle. The system provides a non-conflicting secondary steering system able to assist the primary system when external forces act on the vehicle. A vehicle using this system is able to have larger than usual non-driven wheels, resulting in less design restriction and allowing such things as improved load carrying and distribution of load compared to conventional vehicles of the type. The integration of drive wheel speeds and steer angles of non-driven wheels maximises tractive effort and minimises scuffing losses. The calculation intensive control system for a vehicle described above is only feasible by the availability of relatively low cost microprocessors. Vehicles of this type may be used in agriculture as tractors, harvesters, windrowers and specialised off-road vehicles.