① When the Kobelco excavator performs boom-up operation, the pilot secondary pressure switching boom spool and boom converging spool are input to the low pressure pressure sensor (SE-3) at the same time.
②The output voltage of the low-pressure pressure sensor is input to the electromechanical controller, and the pilot signal is processed internally, and the command current corresponding to the input voltage is input to the P2 cut-off proportional valve (PSV-B).
③ The P2 cut-off proportional valve switches the P2 cut-off spool at the second pressure of the proportional valve corresponding to the command current from the electromechanical controller.
④Due to the switch between the boom spool and the P2 cut-off spool, the negative pressure control pressure fluctuates, and the fluctuating pressure is input to the Pl and P2 negative pressure sensors (SE-26, SE-27) and back pressure sensors (SE-28) .
⑤The output voltage of the Pl, P2 negative pressure sensor and the back pressure sensor are input to the electromechanical controller, and the negative pressure control signal processing is performed internally, and the command current corresponding to the input voltage is output to the Pl pump proportional valve (PSV-P1) and P2 Pump proportional valve (PSV-P2).
⑥Pl pump proportional valve and P2 pump proportional valve change the discharge volume of P1 and P2 pump with the second pressure of proportional valve corresponding to the command current from the electromechanical controller.
⑦The boom spool and the boom merging spool are switched by the pure hydraulic command (pilot 2nd pressure), and the P2 cut-off spool is switched by the electric current hydraulic command (the 2nd pressure of the proportional valve). In this way, the discharge oil of the P2 pump is merged into the discharge oil of the P1 pump during the boom raising operation, and is supplied to the boom hydraulic cylinder.
