Importance

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Abstract

It is an object of the present invention to accurately detect the absorption torque of the other of two hydraulic pumps by a purely hydraulic structure and feed the absorption torque to one of the two hydraulic pumps, thereby to accurately perform a total torque control, effectively utilize a rated output torque of a prime mover, and enhance mountability. To achieve the object, there are provided: a torque feedback circuit 31 to which the delivery pressure of a first hydraulic pump 1a and a load sensing drive pressure are introduced, which modifies the delivery pressure of a second hydraulic pump 1b to provide a characteristic simulating the absorption torque of the second hydraulic pump 1b, and which outputs the modified pressure; and torque feedback pistons 32a, 32b to which the output pressure of the torque feedback circuit 31 is introduced, and which control the capacity of the first hydraulic pump 1a to decrease the capacity of the first hydraulic pump 1a and decrease a maximum torque T1max as the output pressure becomes higher. The torque feedback circuit 31 includes pressure dividing restrictor parts 34a, 34b, pressure dividing valves 35a, 35b, and relief valves 37a, 37b.

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First Claim