Construction machine with working attachment

Abstract

A construction machine, including: a hydraulic pump; a working attachment including a boom, a boom cylinder, and another fluid-supplied cylinder closer to a leading end than the boom cylinder; first and second operation devices for the boom cylinder and the fluid-supplied cylinder; first and second control valves; a flow-rate-limiting section; and an anti-cavitation circuit. The fluid-supplied cylinder receives fluid-supply from the hydraulic pump, together with the boom cylinder. A reaction force upon work accompanying extension of the fluid-supplied cylinder increases the rod-side pressure of the boom cylinder and reduces a head-side pressure. The flow-rate-limiting section limits a supply flow rate to a head-side fluid chamber of the boom cylinder only during a boom-raising-operation with the rod-side pressure higher than the head-side pressure in the boom cylinder. The anti-cavitation circuit replenishes hydraulic fluid from a tank to the head-side fluid chamber.

Description

technical field [0001] The present invention relates to a construction machine including a working attachment such as a hydraulic excavator. Background technique [0002] In a construction machine equipped with a working attachment, the working attachment has a boom, an arm, a working device, a boom hydraulic cylinder for driving the boom, an arm hydraulic cylinder for driving the arm, and an arm hydraulic cylinder for driving the arm. A work hydraulic cylinder of a work device in which a reaction force during work acts on the work attachment in a direction in which the boom cylinder is extended, whereby there is a rod-side oil chamber (rod-side oil chamber) of the boom cylinder. The pressure of the side fluid chamber (hereinafter referred to as the rod-side pressure (rod-side pressure)) increases, and the pressure of the head-side fluid chamber (hereinafter referred to as the head-side pressure (head-side pressure)) falling situation. [0003] use Figure 5 This will be d...

AI Technical Summary

Problems solved by technology

However, this technique involves shrinking the oil chamber from the rod side of the boom cylinder back to the oil tank in order to increase the pressure on the rod side of the boom cylinder to a pressure that can be used as the pressure on the head side of the arm cylinder. Therefore, when the boom cylinder is extended for operations such as horizontal retraction, excess rod side pressure is generated in the boom cylinder and the pressure loss increases.

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