Patent ID: 8056331
Filing Date: 2011-11-15
Classification: E02F,F02D,F04B,F15B

Abstract:
1. A pump torque control system for a hydraulic working machine having: a prime mover, a revolution speed setting means for setting a revolution speed of said prime mover, a prime mover controller comprising an input means for loading the preset revolution speed signal set by said revolution speed setting means, a control means for controlling the revolution speed of said prime mover based on the preset revolution speed signal, an output means for outputting to an outside a signal corresponding an actual revolution speed of said prime mover, and an output means for outputting to said outside a load factor signal corresponding to an output torque of said prime mover, an actuator for driving a movable element, a variable displacement main pump drivable by said prime mover to feed pressure oil to said actuator, a directional control valve for controlling a flow rate and direction of pressure oil to be fed from said main pump to said actuator, a main pump regulator for controlling a displacement volume of said main pump, a variable displacement sub-pump drivable by said prime mover, and a sub-pump regulator for controlling a displacement volume of said sub-pump, wherein: said pump torque control system is provided with: a solenoid-operated proportional valve for said main pump to drive said main pump regulator, and a solenoid-operated proportional valve for said sub-pump to drive said sub-pump regulator, a stroke detector for detecting a stroke of said directional control valve, and a delivery pressure detector for detecting a delivery pressure of said main pump, a main controller comprising an input means for loading the preset revolution speed signal set by said revolution speed setting means, an input means for loading a stroke signal outputted from said stroke detector, an input means for loading a delivery pressure signal outputted from said delivery pressure detector, a positive control means for computing a target displacement volume based on the stroke signal outputted from said stroke detector, a torque limiter means for computing a target absorption torque for said main pump from the preset revolution speed signal outputted from said revolution speed setting means and for computing a target displacement volume for said main pump from the computed target absorption torque and the delivery pressure signal outputted from said delivery pressure detector, a selector means for comparing the target displacement volume computed by said positive control means with the target displacement volume computed by said torque limiter means and for selecting the smaller one as a target displacement volume, an output means for outputting a control signal to said solenoid-operated proportional valve for said main pump based on the target displacement volume selected by said selector means, a computer means for computing a target displacement volume for said sub-pump, and an output means for outputting a control signal to said solenoid-operated proportional valve for said sub-pump based on the target displacement volume for the sub-pump computed by said computer means, and a start means for instructing a start of an adjustment of a maximum absorption torque for said main pump; and said main controller comprises: a first determination means for determining if the setting of the preset revolution speed, which was set by said revolution speed setting means, has been fixed at a rated revolution speed by the instruction from said start means and for outputting a result of the determination, a second determination means for determining, by the instruction from said start means, if the delivery pressure detected by said delivery pressure detector is higher than a predetermined value set beforehand and for outputting a result of the determination, a third determination means for determining, by the instruction from said start means, if the stroke detected by the stroke detector is greater than a predetermined value set beforehand and for outputting a result of the determination, a processor means for switching, when all the determinations by said first, second and third means have resulted in “YES”, the target displacement volume for said sub-pump such that a level of an absorption torque of said sub-pump is set to correspond to a maximum load in use, an input means for loading the load factor signal associated with said prime mover and outputted from said prime mover controller, a processor means for incrementing a target absorption torque for the adjustment at a slow rate from a sufficiently small pump absorption torque, a fourth determination means for determining if a difference between a load factor of said prime mover and the target load factor falls within a predetermined range and for outputting a result of the determination, a processor means for repeatedly performing the loading of the load factor signal and the increment of the target absorption torque for the adjustment as long as the determination by the fourth determination means results in “NO”, a processor means for acquiring, when the determination by said fourth determination means has resulted in “YES”, a target absorption torque at that time and for performing processing that the acquired target absorption torque or a difference between the acquired target absorption torque and a predetermined reference torque is stored as an adjustment value, and a processor means for limiting the target absorption torque, which has been computed by said torque limiter means, by said adjustment value.