The upper turntable of Hitachi excavator is composed of main frame engine, fuel tank, hydraulic oil tank, hydraulic components (hydraulic pump, control valve, etc.), cab and counterweight. The counterweight is bolted to the rear end of the main frame to balance the machine. The front end τ working device is installed on the main frame.
1. Hydraulic pump set
1. Hydraulic spring group structure The hydraulic bag group includes gearbox, main pump and pilot pump, as shown in Figure 5-1.
Engine power is transmitted to the gearbox through the coupling 2, and then to the front 5, rear pump 6 and pilot spring 1. The gear ratio of the three pumps is 1:1:1. The gearbox is lubricated with gear oil. The main pump is an oblique-shaft plunger pump with variable displacement. The main pump includes a front pump 5 and a rear pump 6, and is covered by a casing: the pilot pump 1 is a gear pump. The assembly of the front pump and the rear pump is called the main pump.
The internal structure of the main pump is shown in Figure 5-2. The axis of each elephant is connected to 7 posts inserted into the cylinder. In addition, when the pump shaft rotates, the cylinder also rotates. The rotation of the cylinder body makes the plunger reciprocate in the cylinder tube, so that the hydraulic pump can realize oil absorption and pressure pressing. The shaft 3 and the plunger 6 drive the cylinder 4. The plunger 6 moves in the cylinder of the cylinder 4 and delivers hydraulic oil.
2. Main pump control oil circuit
The main pump control oil circuit is shown in Figure 5-3. Various signals 12 from the pressure sensor (P sensor) 4, the pump displacement angle sensor (A sensor) 3 and the engine speed sensor (N sensor) 9 are input to the controller 11 and the controller 11 determines based on the received signal The pump's current delivery flow rate, and decide whether to increase or decrease, send the appropriate control signal 10 to the pump displacement solenoid valves 6 and 5. The pump displacement solenoid valves 6 and 5 are opened or closed to adjust the position of the servo piston 7 (pump displacement angle), thereby adjusting the output flow of the oil pump. The relationship is shown in Table 5-1.
3. Pilot pump and N sensor, P sensor, A sensor
(1) Pilot pump
The engine rotates the driving gear through the gear transfer box of the main pump. The driving gear drives the driven gear to rotate, driving the pilot
(2) Engine speed sensor (N sensor)
N sensor monitors the engine speed, which is important information for various operation control. The correct installation position of the N sensor is that its end is close to the addendum of the drive gear (the arrangement of the N sensor is shown in Figure 5-4). When a tooth tip passes the top of the N sensor, the N sensor converts this information into a pulsed electrical signal, and the engine speed can be measured based on this pulsed electrical signal
(3) Pressure sensor (P sensor)
P sensor is used to detect oil pressure. Oil pressure is important information for various operation control. When the diaphragm of the sensor is deformed by oil pressure, the P sensor can convert the deformation of the diaphragm into an electrical signal
(4) Pump displacement angle sensor (A sensor)
A sensor layout is shown in Figure 5-5. The A sensor detects the displacement angle by detecting the movement of the shaft 2 and converts it into an electrical signal. The shaft 2 is connected to the cylinder of the main pump through a pin 5 and a lever 1.
