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 ahydraulic 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 heavy excavation mode is selected such as Figure 11 When performing the above-mentioned series of operations in the state shown in (a), it cannot be used according to the changing contents of the work in the series of operations or the operation amount of the control lever, etc., in other words, it cannot be used according to changes in the working conditions. Engine output and pump output vary, so wasteful energy is consumed due to operating 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, if Figure 11 As shown in (c), although unnecessary energy consumption is suppressed by limiting the output power of the pump according to changes in operating conditions, in this series of operations, the engine is on the adjustment line Ra (engine speed NA to Nd). Operating within the range, always in a state of poor fuel consumption rate, resulting in unnecessary fuel consumption

[0011] Additionally, if Figure 11 As shown in (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 matched at the matching points Mc and Md on the adjustment lines Rc and Ra, the The deviation of the absorption torque characteristics of the hydraulic pump (the line width ΔQ indicated by the two-dot chain line in the figure) caused by problems in the manufacture of the hydraulic pump, etc. is proportional to the deviation of the pump absorption power (the power absorbed by the hydraulic pump from the engine) Also remarkably, the desired pump absorbed power cannot be obtained, and workability cannot be ensured satisfactorily.

Images