UG ACTUATOR Caterpillar


UG Actuator Operation

Usage:

Initial Operation

Before starting the engine, make sure the actuator has been installed correctly. Refer to the Installation procedures in this manual. The procedure below should be used in conjunction with the Operation & Maintenance Manual Starting The Engine procedure. Refer to the Operation & Maintenance Manual for more information.

1. Check the oil level of the actuator. Refer to the Operation & Maintenance Section of this manual for more information.

2. Properly adjust the linkage. Refer to the Adjust Linkage story in this manual.

3. Select a LOW SPEED setting to give low engine speed at initial start-up.

------ WARNING! ------

To prevent personal injury, loss of life, and/or property damage when initially starting the engine, be prepared to make an emergency stop. Before starting the engine, make provisions to stop the engine should a runaway or overspeed occur.

--------WARNING!------

4. Start the engine. Refer to the Operation & Maintenance Manual for the complete procedure.

5. Adjust the selected speed setting, as necessary, to bring the engine to rated speed.

6. Obtain system stability.

NOTE: If less than recommended actuator output stroke is used, it may lead to less than optimum engine stability or response.

NOTE: All operating adjustments of the actuator are made during factory calibration. Additional adjustments are not necessary.

Principles of Operation


UG Actuator Schematic Diagram. (1) Terminal Lever. (2) Torque Motor. (3) Loading Spring. (4) Power Piston. (5) Relief Valve. (6) Level Adjust. (7) Range Adjust. (8) Terminal Shaft. (9) Feedback Spring. (10) Torque Motor Beam. (11) Center Adjust. (12) Pilot Valve Plunger. (13) Pressure Reducing Valve. (14) Wash Thru Filter. (15) Gerotor Pump. (16) Drive Input.

The UG actuator consists of the following basic components:

* Oil Pump (Gerotor Pump) (15)- The oil pump is driven by the actuator drive shaft.
* Relief Valve (5)- The relief valve is set to maintain internal operating pressure at 1172 kPa (170 psi).
* Oil Filter- The oil filter filters oil to the pilot valve to prevent contamination of the orifice and nozzle. Bypass oil flows through the filter, providing a filter-cleaning function.
* Torque Motor (2), Torque Motor Beam (10), Feedback Spring (9), and Loading Spring (3)- These items are used to establish a mechanical position of the pilot valve flapper in response to the DC current being sent to the actuator.
* Pilot Valve Plunger (12)- The pilot valve plunger is a follower type valve. The pilot valve plunger duplicates the movement of the torque motor beam, but at a higher force level. The pilot valve plunger controls the flow of oil to and from the servo. The pressure regulator is used to minimize calibration shifts due to speed induced pump pressure changes.
* Power Piston (4), Terminal Lever (1), and Terminal Shaft (8)- The terminal shaft converts linear motion of the differential type servo piston to rotary motion of the terminal shaft. This in turn moves the fuel linkage. The terminal shaft position is fed back to the torque motor beam, which provides the proportional control.

Increase in Load (Speed Setting)

An increase in the load, or the speed setting, causes an increase in control current from the electronic control to the torque motor. This causes an increase in the torque motor force, tending to lower the centering adjustment end of the torque motor beam. The flow of oil through the nozzle is decreased, which increases pressure on the top side of the differential power land. Pressure above the differential power land then moves the pilot valve plunger down (allows the plunger to follow the torque motor beam as if they were one piece). Pressure oil is now directed to the underside of the servo piston, causing it to move upward. When the servo piston moves upward, it rotates the terminal lever and the terminal shaft in the increase fuel direction.

As the terminal shaft rotates, the range adjustment and feedback linkage increases the feedback spring force. This action causes the torque motor beam to move away from the nozzle. As flow through the nozzle is less restricted, pressure decreases on the top side of the differential power land which starts moving the pilot valve plunger up. The terminal shaft and pilot valve plunger movement continues until the increase in feedback spring force equals the increase in force seen in the torque motor. When the pilot valve control land is centered, all movement stops.

Decrease in Load (Speed Setting)

A decrease in the load, or the speed setting, causes a decrease in control current from the electronic control to the torque motor. This causes a decrease in torque motor force, raising the centering adjustment of the torque motor beam. The pilot valve follows the beam and uncovers the control port. Oil trapped under the servo piston drains, causing the servo piston to move downward and the terminal shaft to rotate in the decrease fuel direction.

As the terminal shaft rotates, the range adjustment and feedback linkage decrease the feedback spring force. The terminal shaft rotates until the decrease in spring force equals the decrease in force in the torque motor, and the pilot valve plunger is centered. This stops the servo piston and the actuator shaft in the new (decreased load) position.

Loss of Control Voltage

When control voltage is lost, the actuator terminal shaft automatically goes to minimum fuel. This is a safety feature.

When control voltage is lost, there is no current sent to the torque motor and no magnetic force generated. The torque motor and the torque motor beam, together with the force of the loading spring, causes the center adjustment to rise. The pilot valve follows, keeping the control port uncovered. Trapped oil drains, and the servo piston moves down until it reaches minimum fuel position.

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