M312, M315, M318 and M320 Excavators Hydraulic System Swing Motor Caterpillar


Swing Motor
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Illustration 1g00818156

The swing motor functions in order to drive the swing gear and the upper structure. The swing motor is a fixed displacement axial piston motor.

The swing motor is made up of the following components: input shaft, anti-slip device, piston, rotary group, control lens and end cover with purging device. The swing system is a closed loop hydraulic system. Return oil is returned to the hydraulic tank through a discharge device that is called a purging pump. When the purging pump is actuated, approximately 4.5 L (1.2 US gal) of oil per minute are discharged via the shuttle valve with a pressure relief valve that is installed in the end cover.

Oil from the swing pump directs oil to port (A) or (B). The direction of oil depends on the direction of the swing. Swing pump oil enters the head of the swing motor and the oil passes through the control plate to the barrel.

Pump oil in the cylinder barrel acts against the piston. The piston forces the shoe against the lower plate. The piston and the shoe slide along the inclined surface of the lower plate from the top dead center to the bottom dead center. The force that is created by the shoe and the piston against the lower plate causes the cylinder barrel to rotate. As the barrel rotates each piston passes from the inlet side to the outlet side of the control plate. When the pistons pass the outlet port in the control plate oil in the piston chamber is discharged back to the swing pump.

The swing motor barrel is splined to the output shaft. Rotation of the barrel transmits torque to the output shaft that sends torque to the swing drive.

The flushing valve group is integrated into the control plate. The flushing pin is shifted in order to send some of the oil in the low pressure drive loop to the case of the swing motor. Swing case drain oil flows to the return oil manifold.

Return oil from the pilot manifold enters the swing brake. The swing brake is activated by pilot oil from the swing brake solenoid valve. The solenoid is on the pilot manifold.

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