Hydraulic drive device for working machine

Abstract

The first object is to provide a hydraulic drive device for a working machine, capable of optimally controlling pump absorption horsepower according to change in working condition, thereby reducing fuel consumption. The second object is to provide, on the basis of the first object, to provide a hydraulic drive device for a working machine, capable of suppressing variation in pump absorption horsepower. When working condition determined by a working condition determining section (41) is changed, for example, from working condition (a) to working condition (b), an engine output torque characteristics line (ELa) is switched to an engine output torque characteristics line (ELb) by an engine control device (40a), and a hydraulic pump absorption torque characteristics line (PLa) is switched to a hydraulic pump absorption torque characteristics line (PLb) by a hydraulic pump control device (40b). Further, output torque of an engine (17) and absorption torque of a hydraulic pump (18) are matched to each other at output torque points (Ma, Mb) at which the output of the engine (17) is maximum.

Description

technical field [0001] The invention relates to a hydraulic drive device suitable for being mounted on working machines such as hydraulic excavators. Background technique [0002] As well known, such conventional hydraulic drive devices are disclosed in Patent Documents 1 and 2, for example. In the hydraulic drive device of Patent Document 1, the output torque characteristics of the engine and the absorption torque characteristics of the hydraulic pump are respectively set to suit the work mode selected by the operator. On the other hand, in the hydraulic drive device of Patent Document 2, by detecting a specific operation state of the operation control lever, it is detected that the working machine is in a specific operating state, and when the working machine is in a specific operating state, the corresponding In the operating state, the maximum value of the absorption torque of the hydraulic pump is set to a predetermined value. [0003] Patent Document 1: Japanese Pate...

AI Technical Summary

Problems solved by technology

[0008] However, in the work performed by a hydraulic excavator, for example, when excavating earth and sand, the excavated earth and sand are pocketed into a bucket, the boom is lifted and the upper rotating body is rotated, thereby accumulating the earth and sand in the bucket to a dump truck. In the above case, the required engine output and pump output are very different from the case where the accumulation of soil and sand is completed and the boom is lowered and rotated to move to the next operation cycle.

[0009] However, in the hydraulic drive device of Patent Document 1, there is a problem that when the above-mentioned series of operations are performed in the state shown in FIG. 11( a) in which the heavy excavation mode is selected, the In a series of operations, the content of the work or the amount of operation of the control lever changes at any time. In other words, the output of the engine and the output of the pump cannot be changed according to the change of the working conditions. Therefore, unnecessary energy is consumed due to the working conditions.

[0010] In addition, in the hydraulic drive device of the above-mentioned Patent Document 2, there is the following problem: when performing the above-mentioned series of operations, as shown in FIG. Useless energy consumption is suppressed. However, in this series of operations, the engine operates within the range of the adjustment line Ra (engine speed NA to Nd), and the fuel consumption rate is always poor, resulting in unnecessary fuel consumption.

[0011] In addition, as shown in Figure 11(b) and (c) respectively, there is still the following problem: if the output torque of the engine and the absorption torque of the hydraulic pump are on the matching points Mc, Md on the adjustment lines Rc, Ra Matching is proportional to the deviation of the absorption torque characteristics of the hydraulic pump (the line width ΔQ indicated by the two-dot dash line in the figure) caused by problems in the manufacture of the hydraulic pump, and the pump absorption power (the hydraulic pump absorbs from the engine The deviation of the power) also appears significantly, so that the desired pump absorption power cannot be obtained, and good workability cannot be ensured.

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