Patent ID: 8725364

Claim:
A control device for a hydrostatic transmission vehicle equipped with a hydrostatic transmission including a variable displacement pump to be driven by an engine and a variable displacement hydraulic motor to be rotated by a pressurized oil from the variable displacement pump, the control device comprising: a vehicle speed setting section configured to set a set vehicle speed based on both a forward/rearward travel command and a gear stage command instructed by an operator; a pump and motor displacement control section configured to control respective displacements of the variable displacement pump and the variable displacement hydraulic motor based on the vehicle speed set by the vehicle speed setting section; a hydraulic sensor configured and arranged to detect a pressure in a hydraulic circuit including the variable displacement pump and the variable displacement hydraulic motor; a torque limit setting section configured to obtain an engine speed and set a torque limit usable for the hydrostatic transmission based on the obtained engine speed; a torque control pump displacement setting section configured to set a torque control pump displacement based on the detected pressure in the hydraulic circuit and the torque limit set by the torque limit setting section; a pump displacement selection section configured to select a smaller one of the pump displacement obtained through the control by the pump and motor displacement control section and the pump displacement set by the torque control pump displacement setting section and output the selected one of the pump displacements as a pump displacement command value for controlling the variable displacement pump; a PID control section configured to set the motor displacement for allowing the hydraulic pressure in the hydraulic circuit to be a preliminarily set target pressure by executing a PID control; and a motor displacement selection section configured to select a larger one of the motor displacement obtained through the control by the pump and motor displacement control section and the motor displacement set by the PID control section and to output the selected one of the motor displacements as a motor displacement command value for controlling the variable displacement hydraulic motor.