Patent ID: 6220028
Filing Date: 2001-04-24
Classification: B60W,E02F

Abstract:
A hydraulic drive system for a hydraulic work vehicle, said system being provided with:a motor,a variable displacement hydraulic pump operatively driven by said motor,a first tilting control signal guide system for guiding, as a first tilting control signal, a delivery pressure of said variable displacement hydraulic pump,a second tilting control signal guide system for guiding a second tilting control signal adapted to control torque to be absorbed in said variable displacement hydraulic pump,a unit for generating said second tilting control signal, anda tilting control unit for controlling a displacement of said variable displacement hydraulic pump so that a delivery flow rate of said variable displacement hydraulic pump decreases as a value of said first tilting control signal increases and said torque to be absorbed in said variable displacement hydraulic pump decreases as a value of said second tilting control signal increases, characterized in that said hydraulic drive system comprises:a controller;a unit for outputting to said controller an upper limit signal which determines an upper limit of said torque to be absorbed in said variable displacement hydraulic pump; anda control device arranged in said second tilting control signal guide system and operatively controlled by a drive signal outputted from said controller to perform control so that, when said drive signal is not outputted from said controller, said second tilting control signal is maintained at a predetermined large value and, when said drive signal is outputted from said controller in correspondence to said upper limit signal outputted from said upper limit signal output unit and determining said upper limit of said torque to be absorbed in said pump, said value of said second tilting control signal is changed from said predetermined large value to a small value.