Steerable vehicle

A steerable, self-propelled vehicle including an agricultural tractor, the steerable self-propelled vehicle comprising:

• a steering mechanism having a rotatable steering column that is connected to control a steering angle of one or more ground-engaging members of the vehicle, the vehicle including
• a hydraulic steering servomechanism acting on the steering mechanism in a first location, the hydraulic steering servomechanism having at least a first steering assistance characteristic;
• an electric power steering servomechanism acting on the steering mechanism in a second location, the electric power servo mechanism having a second steering assistance characteristic;
• and
• a programmable controller for causing the first and second steering assistance characteristics to influence the steering of the vehicle in dependence on one or more control commands generated in the controller;
• and
• a human-machine interface (HMI) configured to receive driver input commands selecting two or more programmed modes of operation of the steering servomechanisms,
• wherein the HMI includes respective switches for selecting between programmed modes that control steering during movement of the tractor respectively in a field headland and in other locations, and sequentially selecting sub-modes following selection of a said programmed mode, and
• wherein the sub-modes available following selection of a headland operation include a damped steering sub-mode, a maximal assistance sub-mode, an automatic steering centring sub-mode, and a lock-to-lock assistance sub-mode, and the sub-modes available following selection of other location operation include an on-road sub-mode, a damped steering sub-mode, and a maximal assistance sub-mode.