The automatic two speed walking system has this function only when the walking speed change-over switch is in the two speed position. At this time, the signal makes the travel two speed solenoid valve change direction; at the same time, through the two speed servo cylinder, the travel motor is in the two speed position, and the excavator can travel at high speed.
In addition, the control selection valve is also affected by the walking pressure. When the load is large, such as uphill, the control selection valve reverses to one side of the first speed; the second speed uses the servo control oil pressure to unload, so that the walking motor automatically switches to the first speed position, and the driving force increases. When the excavator is walking on the flat ground or down the slope, the walking resistance becomes smaller, and the control selection valve reverses again, which acts on the two speed servo cylinder, and the walking motor automatically returns to the two speed position, so that the control machine can walk at high speed. Rotary table swing prevention mechanism rotary table swing prevention mechanism is the mechanism to eliminate the swing of excavator rotary table after it stops rotating. Its working principle is: in the process of the rotary horse stopping, both sides of the reverse prevention valve are subject to the unloading pressure, and the spring is compressed. Because the left and right pressures are equal, the reverse prevention valve cannot change direction. When the rotary motor stops running, the pressure at port B is higher than that at port a, which has a reaction force on the rotary motor, and the rotary motor shakes. At this time, the pressure at port a is higher than that at port B, which produces pressure on the reverse prevention valve. Because there is an orifice in the valve, the time lag occurs, and the slide valve moves to the right, so that port a and port B are connected and the pressure is equal. Therefore, the turntable swings only once. There are six executive elements in the hydraulic system of hydraulic excavator: left and right walking motor, rotary motor, boom hydraulic cylinder, stick hydraulic cylinder and bucket hydraulic cylinder. In order to improve the productivity of the excavator and save energy consumption, in the process of digging and loading, the rotary motor and three kinds of hydraulic cylinders need to coordinate action, that is, the control system of the working device should have the following three functions:
(1) Control function of the control machine. Bucket along the horizontal plane or a certain angle with the horizontal plane of linear motion, circular motion; arbitrary trajectory motion.
(2) Loading mining function. Complete full bucket lifting, slewing and unloading. In this process, the bucket is required to maintain the angle at the beginning of lifting relative to the ground level, so as to prevent the materials in the bucket from falling during the lifting process.
(3) Reset control function. After unloading, through the linkage of boom, stick, bucket and slewing, the bucket can be restored to the starting position.