If the machine is equipped with a joystick control, the movement of the joystick control is representative of the movement of the control levers.
The implement ECM electronically controls the solenoid valves (pilot proportioning). Then, the solenoid valves control the movement of the stems in the main control valve for the work tool and any auxiliary hydraulic attachments. The position sensors detect movement in the control levers and the sensors will develop a signal. The implement ECM reads the signals and the implement ECM activates the appropriate solenoid valve (pilot proportioning). As the position sensor begins to rotate, the implement ECM sends a small amount of current to the solenoid valve in order to move the cylinder. As the rotation of the position sensor begins to increase, the implement ECM increases the amount of current to the solenoid valve. Then, the speed of the cylinder will increase proportionally.
The solenoid valve (hydraulic lockout) is activated by the implement ECM whenever the engine is running. The solenoid valve (hydraulic lockout) is an on/off valve that controls the flow of pilot oil through the pilot valve (oil manifold). If the switch (hydraulic lockout) is in the LOCKED position, the implement ECM will not supply current to the solenoid valve (hydraulic lockout).
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| Illustration 1 | g00821751 |
Modulation (Raise) | |
Illustration 1 represents the interpretation by the implement ECM of the signal from the lift lever when the control lever is in the RAISE position. As the control lever is moved from the HOLD position, no current is supplied to the raise solenoid for the lift linkage until the sensor is about 3 degrees from the center. At about 3 degrees of lever travel, the ECM supplies the Start of Modulation Current (1) to the raise solenoid. As the control lever is moved toward the detent, the current that is supplied to the raise solenoid increases. The increase is linear up to Raise Maximum Modulation Current (2). The maximum modulation current is reached just before the control lever enters the detent position. Entering the detent position will not cause a further increase in the current.
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| Illustration 2 | g01194758 |
Modulation (Lower) | |
Illustration 2 represents the interpretation by the implement ECM of the signal from the lift lever when the control lever is in the LOWER position. As the control lever is moved away from the center, no current is supplied to the solenoid valve until the control lever is about 3 degrees from the center. At about 3 degrees of travel by the lever, the implement ECM supplies the Start of Modulation Current (3) to the lower solenoid. As the control lever is moved toward the detent, the current that is supplied to the lower solenoid increases. The increase is linear up to Lower Maximum Modulation Current (4). The maximum modulation current is reached just before the control lever enters the detent position. As the position sensor is moved into the detent position, the implement ECM will increase the current. The current will increase until pilot pressure shifts the main valve into the FLOAT position.
Note: The Start of Modulation Current provides pilot pressure in order to shift the main valve spool. When the main spool is shifted, hydraulic oil will flow to the cylinders. The Start of Modulation Current varies for each valve. The Start of Modulation Current must be adjusted for each valve. The modulation current must be calibrated on each individual machine.
Note: The Maximum Modulation Current provides enough pilot pressure in order to shift the main valve spool. When the main valve spool is shifted fully, the cylinder will reach maximum velocity.
ReferenceFor additional information about using Caterpillar Electronic Technician in order to calibrate the modulation currents, refer to the Service Manual module Testing and Adjusting, "Main Control Valve (Electronic Technician) - Calibrate" for the machine that is being serviced.
ReferenceFor additional information about using the Operator Monitoring System to calibrate the modulation currents, refer to the Service Manual module Testing and Adjusting, "Main Control Valve (Operator Monitor) - Calibrate" for the machine that is being serviced.