Patent ID: 7987941
Filing Date: 2011-08-02
Classification: B60W,F16H,Y10T

Abstract:
1. A construction vehicle comprising: an engine; a hydraulic pump configured and arranged to be driven by the engine; a travel hydraulic motor configured and arranged to be driven by pressure oil discharged from the hydraulic pump; a primary circuit through which the pressure oil flows from the hydraulic pump to the travel hydraulic motor; travel wheels configured and arranged to be driven by drive force of the travel hydraulic motor; and a controller configured to control an engine speed, displacement of the hydraulic pump, and displacement of the travel hydraulic motor in order to control a vehicle speed and traction force, the controller being configured to vary the displacement of the travel hydraulic motor between an upper-limit displacement and a lower-limit displacement according to a pressure of the pressure oil in the primary circuit with the upper-limit displacement being set to be equal to or smaller than a ceiling displacement determined based on performance of the hydraulic motor, the controller being further configured to increase the upper-limit displacement of the travel hydraulic motor as the vehicle speed decreases in a low vehicle speed range from zero to a predetermined threshold to obtain vehicle speed/traction force characteristics with which a maximum traction force is substantially maintained in the low vehicle speed range.