Hitachi Construction Machinery Co., Ltd.

Shohei Sugiki

Kenji Hiraku

Hiromasa Takahashi

Juri Shimizu

Teppei Saitoh

Provided is a construction machine in which travel operability is not impaired when a combined operation is performed in which a single-rod hydraulic cylinder is driven during a travel operation. A hydraulic excavator includes a controller that controls the delivery direction and delivery flow rate of a closed-circuit pump, opens and closes a travel switching valve and an assist switching valve, and controls the delivery flow rate of the open-circuit pump, according to a travel operation lever and a work operation lever. The controller holds the assist switching valve in a closed position irrespective of whether or not the work operation lever is operated in a case where the travel operation lever is operated.

Construction machine

Provided is a work machine that can selectively establish a closed circuit connection between a single rod-type hydraulic cylinder and a plurality of bidirectional-type hydraulic pumps, the work machine being capable of enhancing responsiveness of the single rod-type hydraulic cylinder when a high-speed lever switching operation is conducted in a state in which a rod pressure of the single rod-type hydraulic cylinder is higher than a bottom pressure. When a bucket lever () is operated to a side of extending the bucket cylinder in a state in which a pressure in a rod chamber () of the bucket cylinder () is higher than a pressure in a bottom chamber (), a controller () opens a rod-side proportional valve () and discharges a working fluid in the rod chamber to a working fluid tank () such that a differential pressure between the pressure in the rod chamber and the pressure in the bottom chamber is reduced below a switching pressure (Psw) of a flushing valve ().

Drive system for construction machine

A construction machine is provided which includes a hydraulic closed circuit in which a single rod hydraulic cylinder is driven directly by a bidirectionally tiltable variable displacement pump and can stably speed up the contraction action of the single rod hydraulic cylinder. In the case where a contraction action of a hydraulic cylinderis instructed through an operation leverwhen a differential pressure obtained by subtracting the pressure of a cap chamberfrom the pressure of a rod chamberis equal to or lower than a first threshold value a set to a level equal to or higher than a selection setting pressure of a flushing valvea controllercloses a rod side selector valveto disable rod assist action for supplying hydraulic fluid from a second hydraulic pumpto the rod chamber, and when the differential pressure is higher than the first threshold value, the controlleropens the rod side selector valve to enable the rod assist action.

A drive system for a construction machine capable of appropriately controlling a distribution flow rate to each hydraulic actuator and improving operability by an operator is provided. A flow rate distribution section that computes a distribution flow rate of a hydraulic fluid supplied to each of a plurality of hydraulic actuators on the basis of a demanded flow rate, sets, within a distributable region set for computing a range of a distributable flow rate that is a flow rate of the hydraulic fluid suppliable to each of at least two hydraulic actuators driven by a combined operation among the plurality of hydraulic actuators from a plurality of hydraulic pump devices for the at least two hydraulic actuators, a distribution region for computing a range of the distribution flow rate of the hydraulic fluid actually supplied to each of the at least two hydraulic actuators, and computes the distribution flow rate in such a manner that the distribution flow rate falls within the distribution region and a ratio among the distribution flow rates of the plurality of hydraulic actuators is equal to a ratio among the demanded flow rates of the plurality of hydraulic actuators.

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Tsuchiura, Japan

Shohei Sugiki