Hydraulic system for small-sized excavator to improve bucket speed

摘要

A hydraulic system for a compact excavator is provided to speed up a bucket in a single or compound operation by employing a converging valve for converging flows of first and second pumps. A hydraulic system for a compact excavator comprises first and second pumps(10,11), a first line(51), a first control valve group, a second line(53), a second control valve group, and a converging valve(2). The first line conveys discharge oil pressure of the first pump. The first control valve group includes a right traveling spool(21), a boom second speed spool(22), and an arm first speed spool(23) which are installed on a first center bypass line connected with the first line. The second line conveys discharge oil pressure of the second pump. The second control valve group includes a left traveling spool(24), a boom first speed spool(25), an arm second spool(26), and a bucket spool(27) which are installed on a second center bypass line connected with the second line, wherein the bucket spool is locates at the lowest part. The converging valve contacts with the first line and the second line respectively and provided with a convergence position and a convergence relief position for the first line and the second line. A pressure receiving unit at the convergence position is connected with a bucket spool control pilot signal line(Pi4). A opposing pressure receiving unit is connected with a pilot signal line(Pi3) generated when one of the boom, the spool, and the traveling spool of the first and second valve groups is operated. The convergence valve is switched to a convergence position or a convergence relief position by the difference between pressures of both pressure receiving units.