Working machine

Abstract

A working machine includes a hydraulic control apparatus. In a straight travel valve of the hydraulic control apparatus, a communication path and a control valve that opens and closes the communication path are provided. During a combined operation of traveling operation and working operation, a working pressure and a traveling pressure are taken in as pilot pressures on either side. During a small traveling operation in which the traveling operation amount is small, the communication path is unconditionally closed. During a large traveling operation in which the traveling operation amount is large, if the working pressure is higher than the traveling pressure, the communication path is open, and if the working pressure is lower than the traveling pressure, the communication path is closed.

1 . A working machine comprising: 
 a lower traveling body;    an upper rotating body mounted on the lower traveling body;    a working attachment attached to the upper rotating body;    hydraulic actuators including working actuators that actuate the working attachment, and right and left traveling motors, the hydraulic actuators being separated into a first group including one of the right and left traveling motors and a second group including the other traveling motor;    first and second pumps serving as hydraulic pressure sources;    a straight travel valve adapted to switch the flow lines of discharged oils from the pumps, the straight travel valve being at a neutral position to supply the first and second groups with discharged oils of separate pumps during a single operation in which traveling operation and working operation are performed separately, being switched to a straight travel position to supply both traveling motors and the working actuators with discharged oils of separate pumps during a combined operation in which traveling operation and working operation are performed simultaneously, and enabling pump lines of both of the pumps to communicate with each other via a communication path in the process of switching of the straight travel valve from the neutral position to the straight travel position; and    a control valve adapted to open and close the communication path, wherein, during the combined operation, the control valve controls the communication path according to the position of the straight travel valve, a working pressure that is an actuating pressure of the working actuators, and a traveling pressure that is an actuating pressure of the traveling motors, in the following manners:    (I) during a small traveling operation in which the traveling operation amount is smaller than a predetermined value, the communication path is unconditionally closed; and    (II) during a large traveling operation in which the traveling operation amount is larger than the predetermined value, if the working pressure is higher than the traveling pressure, the communication path is open, and if the working pressure is lower than the traveling pressure, the communication path is closed.    
   
   
       2 . The working machine according to  claim 1 , wherein, when the straight travel valve is switched to the straight travel position, the communication path is unconditionally closed.  
   
   
       3 . The working machine according to  claim 1 , wherein the control valve is a hydraulic pilot valve, the working pressure is introduced into a first pilot chamber of the control valve, and the traveling pressure is introduced into a second pilot chamber.  
   
   
       4 . The working machine according to  claim 2 , wherein the control valve is a hydraulic pilot valve, the working pressure is introduced into a first pilot chamber of the control valve, and the traveling pressure is introduced into a second pilot chamber.  
   
   
       5 . The working machine according to  claim 3 , wherein the communication path and a sub-spool are provided in a main spool that is a spool of the straight travel valve, the first pilot chamber and the second pilot chamber are formed on either side of the sub-spool, a working side pilot port that introduces the working pressure into the first pilot chamber and a traveling side pilot port that introduces the traveling pressure into the second pilot chamber are provided in the main spool, and the communication path, the sub-spool, the first pilot chamber, the second pilot chamber, the working side pilot port, and the traveling side pilot port constitute the control valve.  
   
   
       6 . The working machine according to  claim 4 , wherein the communication path and a sub-spool are provided in a main spool that is a spool of the straight travel valve, the first pilot chamber and the second pilot chamber are formed on either side of the sub-spool, a working side pilot port that introduces the working pressure into the first pilot chamber and a traveling side pilot port that introduces the traveling pressure into the second pilot chamber are provided in the main spool, and the communication path, the sub-spool, the first pilot chamber, the second pilot chamber, the working side pilot port, and the traveling side pilot port constitute the control valve.