The figure is the schematic diagram of Nachi travel motor of yc35-6. A. B is the working oil port, PP is the travel motor speed change (fast and slow) interface, which is connected with the travel speed change valve, and Dr is the oil return port, which is connected with the oil tank. The working pressure of the travel motor is 21MPa.
If the working pressure oil enters the brake valve from port a, the pressure oil pushes the valve core along the control oil circuit at end a to change the valve to the working position at end A. part of the pressure oil enters the brake cylinder through the mechanical brake control oil circuit to open the mechanical brake mechanism of the motor. The main pressure oil enters the motor to make the motor rotate back, and the return oil of the motor returns to the oil tank through the brake valve. If the traveling motor is out of control (sliding), the oil inlet is insufficient, the pressure of the control oil circuit decreases, the brake valve core returns to the middle position under the action of the spring, and the oil return channel is turned down (or closed), so that the motor slows down (or stops), ensuring safe traveling.
The travel motor assembly is composed of a plunger swing motor and a planetary reducer.
The system working pressure is 21MPa, the slewing working pressure is 16.7mpa, and the working pressure of the pilot control oil circuit is 4MPa. 21MPa safety valves are installed at the two oil inlets of the multi-way valve respectively. The overload valves on the boom and stick reversing valves are set to a pressure of 24MPa. Single direction throttle valves are installed on the oil return circuit of the boom cylinder cavity to prevent the boom from falling too fast due to its own weight. Two 16.7mpa buffer valves are installed on the inlet and outlet oil circuits of the slewing motor, The oil circuit of the traveling motor is equipped with a brake valve to prevent the excavator from speeding down the slope.
The hydraulic system is also equipped with a low-pressure oil drain circuit to make the hydraulic motor and the central swivel leak oil back to the oil tank.
The variable control signal of the variable displacement pump comes from the pump outlet pressure P1 and P2. When the pump idles at the rated speed (2200 RPM), the oil output from the oil pump returns to the oil tank from the middle passage of the multi-way directional valve. At this time, the oil output flow of the oil pump is the maximum. When the excavator is operated, P1 and P2 begin to increase. When p1+p2=8.7mpa, the variable piston of the pump pushes the variable swashplate of the pump, and the variable displacement pump starts to change. The larger p1+p2, the smaller the pump output flow until p1+p2=42mpa, At this time, the oil pump output oil flow is minimum.
