Hydraulic control system in working machines

Abstract

In a working machine in which a replaceable working attachment is attached to a tip portion of a working arm including a boom, even when the working attachment is replaced, lowering the boom at a lowering speed corresponding to an operation amount of an operating tool is controlled in a stable state. A monitor device for inputting information relating to a weight of an attached working attachment to a controller is provided. A map indicating a relationship between the weight of the replaceable working attachment (8) and a holding pressure of a boom cylinder head side oil chamber is provided in a controller. A holding pressure estimated value corresponding to the weight of the attached working attachment is obtained, based on the map. A configuration is adopted so that an opening area of a contraction side discharge opening of a control valve is controlled based on the holding pressure estimated value.

1 . A boom lowering control system in a working machine including a working arm including at least a boom pivotally supported to be vertically swingable on a machine body; a replaceable working attachment attached to a tip portion of the working arm; a boom cylinder that causes the boom to vertically swing by expanding through oil supply to a head side oil chamber and contracting through oil discharge from the head side oil chamber; a control valve having a meter-out opening for controlling a discharge flow rate from a boom cylinder head side oil chamber; control means for controlling an operation of the control valve; and an operating tool operated to vertically move the boom, the boom lowering control system comprising:
 information input means for inputting information relating to a weight of the attached working attachment to the control means,   wherein the control means includes a map indicating a relationship between the weight of the replaceable working attachment and a holding pressure of the boom cylinder head side oil chamber, and obtains a holding pressure estimated value corresponding to the weight of the attached working attachment based on the map, and   based on the holding pressure estimated value, the control means controls a meter-out opening area of the control valve so that the discharge flow rate from the boom cylinder head side oil chamber becomes a target discharge flow rate set in accordance with an operation amount of the operating tool when the boom is lowered.   
     
     
         2 . The boom lowering control system in a working machine according to  claim 1 , wherein when the holding pressure estimated value corresponding to the weight of the attached working attachment is obtained, based on the map, the control means groups a holding pressure map value of the boom cylinder head side oil chamber into a plurality of groups in accordance with a magnitude of the holding pressure map value to set a representative value of the holding pressure in advance for each group and to set the holding pressure representative value of a group to which the holding pressure map value corresponding to the weight of the attached working attachment belongs, as the holding pressure estimated value corresponding to the weight of the attached working attachment. 
     
     
         3 . The boom lowering control system in a working machine according to  claim 1 , wherein when the holding pressure estimated value corresponding to the weight of the attached working attachment is obtained, based on the map, the control means sets a representative value of the holding pressure in advance for each group by grouping the working attachments into a plurality of groups in accordance with a magnitude of the weight of the working attachment, and sets the holding pressure representative value of a group to which the attached working attachment belongs, as the holding pressure estimated value corresponding to the weight of the attached working attachment. 
     
     
         4 . The boom lowering control system in a working machine according to  claim 1 ,
 wherein the map uses a linear relationship to indicate a relationship between the weight of the working attachment and the holding pressure of the boom cylinder head side oil chamber, based on a moment around a support shaft for pivotally supporting the boom to be swingable on the machine body.   
     
     
         5 . The boom lowering control system in a working machine according to  claim 1 , wherein the weight of the working attachment includes a weight of a coupler used to attach the working attachment to the tip portion of the working arm. 
     
     
         6 . The boom lowering control system in a working machine according to  claim 1 , wherein the working arm includes the boom and a stick pivotally supported to be swingable in a tip portion of the boom,
 a working attachment attached to the tip portion of the boom and a working attachment attached to a tip portion of the stick are provided as the working attachment, and   the map when the working attachment is attached to the tip portion of the boom and the map when the working attachment is attached to the tip portion of the stick are individually provided.