Swing Motor Operation

148

When the swing joystick is partially shifted, the pilot pressure oil from the swing pilot valve cannot overcome the swing priority valve spring to move the the valve spool left. The swing priority valve spool does not restrict oil to the stick 1 control valve as shown in this illustration.

Unrestricted flow from the idler pump is available to the stick 1 control valve to operate the stick.

When the swing pilot valve is fully shifted, pilot oil pressure moves the swing priority valve spool to the right against spring force. With the swing priority valve spool moves to the left, supply oil to the stick 1 control valve is restricted and the stick cylinder speed is reduced.

149

Swing MotorOperation

The swing motor may be divided into the following three groups :

- The rotary group: piston and barrel assembly, shoes, retainer plate, and drive shaft.

- The parking brake: brake spring, brake piston, separator plates, and friction plates.

- The relief valves and makeup valves.

When a swing operation is started, pilot oil from the swing brake solenoid valve is directed to the swing brake piston. As the pilot pressure builds, the brake piston moves against the spring to release the swing brake. The brake separator plates and friction plates are no longer in contact and the motor barrel assembly can rotate freely.

During a SWING RIGHToperation, the oil delivery enters the motor head from the swing control valve and flows through a plate in the motor into the piston and barrel assembly to cause the motor to rotate.

Return oil flows back from the motor to the motor head and back to the swing control valve to return to the tank.

As pressure increases in the fill chamber, the piston moves to the left. As the piston moves to the left, oil in the dampening chamber is forced out of the orifice in the piston. This feature modulates the movement of the piston to the left to gradually compress the the relief valve spring to increase the relief valve setting.

In a swing stall condition, the piston is moved fully to the left to compress the spring even more. The swing relief valve is at the maximum setting.

150

The swing parking brake is located in the swing motor. The swing parking brake consists of the following components: brake spring, brake piston, separator plates, and friction plates. The friction plates are splined to cylinder barrel. The separator plates are splined to the motor case.

When the joysticks are moved from the NEUTRALposition, the implement pressure switch senses the increase in pilot oil pressure. The pressure switch closes and sends an input signal to the Machine ECM. The Machine ECM energizes the swing brake solenoid valve.

When the swing brake solenoid valve is energized, the spool moves down against the spring. Pilot oil flows to the center of the spool and out to the swing motor.

The pilot oil now enters the piston chamber. The pilot pressure causes the brake piston to move upward against the force of the brake spring. The separator plates and friction plates are no longer held together and the motor is able to rotate freely.

151

When the joysticks are returned to the NEUTRALposition, idler pump supply oil to the swing motor is stopped. The implement pressureswitch senses the decrease in pilot oil pressure. The implement pressure switch opens. The Machine ECM senses the change in state of the implement pressure switch and de-energizes the swing brake solenoid valve.

The spool is moved upward by the force of the spring in the solenoid valve. The spool blocks pilot oil flow from flowing to the brake piston. Oil in the brake piston is open to the tank through the swing brake spool.

The brake spring moves the brake piston down to press the separator plates and friction plates together to apply the swing parking brake.

Since the Machine ECM does not de-energize the swing brake solenoid valve until approximately 6.5 seconds after the swing joystick is returned to the NEUTRALposition, the rotation of the swing motors stops hydraulically before the swing brake is engaged.

If the solenoid is de-energized before the rotation of the swing motors stops, damage and wear to the swing parking brake would result.

152

Two dual stage, swing relief valves are located in the head of the swing motor. These relief valves limit the maximum pressure in the left and right swing circuits. The pressure setting of the swing relief valves is less than the pressure setting of the main hydraulic relief valve.

The dual stage, swing relief valves open initially at a lower pressure to reduce jerkiness in the swing circuits at swing start and swing stop or to handle short duration pressure spikes.

The relief valves also allow for higher swing circuit pressures to provide increased swing force. The higher relief valve setting is modulated up to the relief valve maximum.

In NEUTRAL, spring force moves the stem to the left to the closed position and moves the piston to the right against the stop.

At the start of the swing operation or if a pressure spike occurs, system pressure moves the stem to the right, which opens the work port to drain. Oil also flows through the orifice in the left end of the stem to the chamber at the right end of the stem to the fill chamber on the right end of the piston.

153

When the swing joystick is moved to stop the swing while swinging right, the swing control valve shifts to the NEUTRALposition. Since the swing control valve is in the NEUTRAL position, the supply oil and return oil passages to motor rotary group are blocked at the swing control valve.

Due to inertia, the upper structure will attempt to continue to rotate.

Avacuum is created on the supply side of the motor, while the return side is pressurized.

The line relief opens and allows oil in the high pressure side to enter the drain line to the slow return check valve.

The slow return check valve creates a back pressure and helps to force open the makeup valve in the low pressure line to the rotating group.

154

Return oil from the main control valve group and from the swing motor group flows into the housing for the slow return check valve as shown in the above illustration.

The back pressure created by the slow return check valve ensures that makeup oil is present at the swing motor and the various makeup valves in the hydraulic system.

After flowing through the slow return check valve oil flows to the cooler inlet line and the bypass check valve. At low temperatures, the high viscosity of the oil flowing through the hydraulic oil cooler causes the pressure to rise. The rising pressure causes the bypass check valve to open. Most of the oil flows through the bypass check valve. Because only a small amount of oil flows through the cooler, the oil temperature increases.

As the oil temperature increases, the bypass check valve begins to close and a greater portion of the oil flows through the hydraulic oil cooler. The bypass check valve maintains the oil at the optimum operating temperature.

155

The anti-reaction valves are used to eliminate the reverse swing effect when the swing operation is stopped. When the swing hydraulic control valve is returned to NEUTRAL, the upper structure continues to rotate due to inertia. Without the anti-reaction valve, the swing motor acts like a pump and a hydraulic lock is formed in the swing lines between the motor and the swing control valve. This pressure causes the swing motor to turn the upper structure in reverse slightly after the upper structure is stopped.

When the swing control valve is returned to NEUTRAL, pressure increases and is directed to the anti-reaction valve. The anti-reaction valve shifts to connect the outlet passage to the inlet passage through the valve allowing pressure oil to move to the low pressure side. As the upper structure slows to a smooth stop, pressure in the high pressure side decreases, allowing spring force to return the anti-reaction valve to the NEUTRALposition.

156

This sectional view shows the anti-reaction valve in the ACTIVATED position. When the swing control valve is returned to NEUTRAL, the upper structure continues to swing. Pressure increases in the right side of the valve because of the pumping action of the swing motor. The pressure goes through the orifice to the center of the anti-reaction valve and to the spring chamber on the right end of the valve. As pressure increases, the valve moves slowly to the left until it contacts the retainer. Before the valve contacts the retainer, high pressure oil passes through the internal passages (shown by the arrow) to the "suction" side of the motor.

The internal passage allows the pressure on each side of the motor to become equal. As the pressure on each side of the motor becomes balanced, the upper structure slows to a complete stop with no backlash in the swing gears.

157

The swing drive consists of a series of planetary gears. The planetary gears reduce the rotational speed of the swing motor. The swing motor is bolted to the top of the swing drive. The swing drive is bolted to the upper structure. The teeth of the swing drive output pinion shaft engage with the bearing gear of the swing bearing. The pinion shaft rotates around the bearing gear. This rotation causes the machine to swing. The bearing gear is attached to the lower structure.

The swing drive is divided into the following two groups : - The first group provided a double reduction of motor speed. The components of the first stage reduction are the first stage sun gear, the first stage planetary gears, the ring gear, and the first stage planetary carrier. The components of the second stage reduction are the second stage sun gear, the second stage planetary gear, the ring gear, and the second stage planetary carrier. - The second group reduces output speed of the motor. The components of the second group are the roller bearings and the pinion shaft. The roller bearings are installed in the housing and support the pinion shaft.

The swing speed is reduced by a ratio of teeth on the sun gear to ring gear teeth by planetary reduction. Since the sun gear is inside of the ring gear, the swing drive is more compact than the reduction units with external teeth.

158

The swing motor output shaft is splined to the first stage sun gear. The first stage planetary gears of the first stage planetary carrier mesh with the first stage sun gear. When the first stage sun gear rotates counterclockwise, the first stage planetary gears rotate in a clockwise direction on shafts.

The first stage planetary gears move counterclockwise around the ring gear. The ring gear is bolted to the housing. The first stage planetary carrier rotates counterclockwise.

159

Splines on inner circumference of the first stage planetary carrier engage with the splines on the second stage sun gear. This engagement causes the second stage sun gear to rotate counterclockwise when the first stage planetary carrier rotates.

The second stage planetary gears turn clockwise on the shafts. The second stage planetary gears move in a counterclockwise direction around the ring gear.

The second stage planetary carrier turns counterclockwise around the ring gear. The splines on the inner circumference of second stage planetary carrier engage with the splines of pinion shaft. When the second stage planetary carrier turns clockwise, the pinion shaft rotates counterclockwise.

160

The pinion shaft engages with the bearing gear on the inner circumference of the swing bearing. The bearing gear is bolted to the lower structure.

As the pinion shaft rotates counterclockwise, the pinion shaft moves in a clockwise direction around the bearing gear.

The upper structure also rotates in a clockwise direction around bearing gear. This rotation causes the upper structure to swing to the right (clockwise rotation).

NOTES