CAM 7K7123 - Caterpillar

Implement Control Solenoid Valves (Raise, Lower, Tilt Back, Dump) - Auxiliary Third Function Solenoid Valves (Port A, Port B)
To control the proportional solenoid valves in the electrohydraulic implement control system, the Implement ECM will use PWM driver circuits for each solenoid.The ECM will use a Pulse Width Modulated (PWM) signal to energize the solenoids. The ECM will vary the duty cycle of the PWM signal in order to control the amount of electrical current that is sent to the proportional solenoids. As the duration of the high signal increases, the percentage of the duty cycle and the amount of electrical current in the circuit will increase.A PWM duty cycle is the percentage of time that the signal is "High" compared to the amount of time that the signal is "Low" for a complete cycle.For the control of the implement system solenoid valves, the ECM will apply a current amount that corresponds to the input signals from the operator controls. The current in the solenoid coil windings moves the valve plunger to allow a proportional amount of pilot pressure to act on one end of the valve spool. The position of the valve plunger controls the amount of pilot oil at the end of the valve spool. The shifting of the valve spool works against pilot pressure that is acting against the spool movement on the other end of the valve spool. The spool will modulate or move back and forth. This modulation controls the amount of pressure that is present at the valve output port.An increase in ECM current to a solenoid results in changing modulation of the spool. More hydraulic oil pressure and flow are directed to the hydraulic cylinders. This increased pressure and flow will cause the rate of movement of the implement to increase. As the ECM decreases the current to a solenoid, the pilot oil flow decreases, the changing modulation of the spool allows less hydraulic oil flow to the hydraulic cylinders. The movement of the implement will decrease.The four implement control solenoid valves and the auxiliary control solenoid valves are identical. The resistance of a good solenoid coil is 5 0.3 ohms at 25° C (77° F). Resistance is slightly affected by operating temperature. Resistance will increase as temperatures increase.Lower Anti-Drift Solenoid Valve, Dump Anti-Drift Solenoid Valve
The anti-drift solenoids valves are identical 24 VDC ON/OFF solenoid valves. The Implement ECM energizes the solenoids with 24 VDC ON / Off driver circuits.When the implement control lever or joystick is moved to the LOWER position, in addition to energizing the lower solenoid valve, the Implement ECM will turn ON the circuit for the Lower Anti-Drift Solenoid Valve. The oil from the head end of the lift cylinders will drain to tank through the valve spool. When the Lower Anti-Drift Solenoid Valve is de-energized, a check valve prevents oil flow out of the head end of the lift cylinders.When the implement control lever or joystick is moved to the DUMP position, in addition to energizing