Vehicle control system

A vehicle control system, comprising:

• an engine;
• a hydro-mechanical transmission constructed such that power from the engine is transmitted from an input shaft to an output shaft through a mechanical transmission unit and a hydrostatic transmission unit;
• engine controlling means for controlling the engine;
• and
• decelerating means for outputting a deceleration command in accordance with an amount by which the decelerating means is operated;
• wherein, in a lower speed region of the engine, a first torgue transforming is carried out such that the hydro-mechanical transmission generates, from the output shaft, a first output torque which matches a first tractive force required by a given load, while setting a first engine output torque value corresponding to a first engine speed in the lower speed region as a first input torque value and keeping said first input torque value constant, and a first tractive force-vehicle speed characteristic in the lower speed region is set based on said first torgue transforming in the lower speed region,
• wherein, in a higher speed region of the engine, a second torgue transforming is carried out such that the hydro-mechanical transmission generates, from the output shaft, a second output torque which matches a second tractive force required by the given load, while setting a second engine output torque value corresponding to a second engine speed in the higher speed region as a second input torque value and keeping said second input torque value constant, and a second tractive force-vehicle speed characteristic in the higher speed region is set based on said second torgue transforming in the higher speed region, and
• wherein a third tractive force-vehicle speed characteristic corresponding to a direct region is set, and the direct region is an engine speed region between said first engine speed in the lower speed region and said second engine speed in the higher speed region, in which power from the input shaft is transmitted to the output shaft through the mechanical transmission unit alone, and
• wherein the engine controlling means controls the engine so as to reduce, in response to the deceleration command from the decelerating means, the engine output torque which corresponds to an engine speed region between said first engine speed in the lower speed region and said second engine speed in the higher speed region including said first and second engine speed.