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| Illustration 1 | g00952764 |
The cooling system is a hydraulically driven fan, that is controlled by an on demand fan control system. The on demand fan system controls the fan speed in order to provide the required amount of cooling air. This will maintain key system temperatures. During heavy machine usage or high ambient temperatures, the on demand fan system will increase the fan to the maximum speed. During light usage and lower ambient temperature, the on demand fan system will maintain a lower fan speed. This can result in lower horsepower requirements. The on demand fan controls the speed of the fan system through the use of a variable displacement piston pump. This will vary the volume of hydraulic oil to the fan motor. The volume of oil that is produced by the hydraulic fan pump is controlled by the pressure and flow compensator valve.
The pressure and flow compensator valve that controls the pump flow is mounted below the hydraulic fan pump. The pressure and flow compensator valve contains the flow control spool and the pressure cutoff spool. The flow control spool will control the minimum fan speed to the maximum fan speed. The maximum fan speed is controlled by the cutoff spool. Pressure cutoff spool 11 also controls the maximum pressure of the hydraulic fan pump. The settings of the flow control spool and the cutoff spool are adjustable.
The engine ECM receives inputs from four sensors that are installed on the machine. Four sensors monitor the engine air inlet temperature, the coolant temperature, the hydraulic oil temperature, and the transmission oil temperature.
The engine ECM interprets the data from the four sensors. The logic for the on demand fan is compared against a set of target temperatures.
If one temperatures exceed the target temperture, the engine ECM will send a signal to the solenoid valve in order to increase the fan speed. If one of the temperatures is less than the target temperture, the engine ECM will send a signal to the solenoid valve in order to decrease the fan speed.
If the temperature at one of the sensors increases, the engine ECM sends a proportional reduction in current to the solenoid valve in the on demand fan system. Then, the solenoid valve sends a reduced hydraulic signal to the pressure and flow compensator valve on the piston pump. The hydraulic fan pump will adjust the pump output flow for the demand.
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| Illustration 2 | g00952767 |
When the engine is first started and the hydraulic oil is cold, the oil from the piston motor can not easily flow through the hydraulic oil cooler. The oil pressure will increase in the hydraulic oil cooler. The check valve for the hydraulic oil cooler bypass will open. The check valve limits the maximum oil pressure in the oil cooler to 450 ± 55 kPa (65 ± 8 psi). The oil from the case drain is filtered through a screen in the hydraulic oil tank.
As the hydraulic oil temperature increases, the pressure of the oil through the oil cooler will decrease. The force of the spring in the check valve (hydraulic oil cooler bypass) is greater than the force of the oil pressure. Then, the check valve will close. The hydraulic oil will flow through the oil cooler into the hydraulic tank.
When the engine is started, all temperatures for the four sensors are below the key target temperatures. The engine ECM sends the maximum current to the solenoid valve. Signal oil to the flow control spool is open to the hydraulic tank through the solenoid valve. Supply oil is directed to the actuator piston in order to destroke the pump. The angle of the pump swashplate is at a minimum. The pump will produce a minimum flow.
As one of the temperatures of the four sensors increases above the key target temperature, the engine ECM sends a proportional reduction in current to the solenoid valve. The solenoid valve will start to shift. This will allow some of the supply oil to flow to the flow control spool. The flow control spool starts to shift to the left. A proportional amount of oil that is on the right side of the actuator piston will flow back to the hydraulic tank. As the pressure behind the actuator piston begins to decrease, the actuator spring will increase the swashplate angle. The pump output flow will increase. The fan speed will increase.
As the temperatures of the machine continue to increase, the engine ECM will continue to reduce the current that is sent to the solenoid valve. The solenoid valve will continue to shiftin the downward direction. This will increase the hydraulic signal to the flow control spool. The control spool will shift more to the left in order to continue to drain oil that is behind the actuator piston. The swashplate moves more toward a maximum angle and the pump flow continues to increase. The fan speed continues to increase.
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| Illustration 3 | g00952768 |
If the current from the engine ECM to the solenoid is at a minimum, the solenoid valve will send the maximum hydraulic signal to the flow control. Pump output flow will increase due to the swashplate that is moving toward the maximum angle.
As the rpm of the hydraulic fan motor approaches the maximum speed,the pressure of the pump output also increases. The increase in pressure of the pump supply oil will work on the left side of both the flow control spool and the pressure cutoff spool. The flow control spool will stay to the left. The pressure on the left side of the cutoff spool will overcome the spring. The cutoff spool will start to shift to the right. This will allow some of the pump supply oil to flow to the actuator piston. This will slightly destroke the pump in order to reduce pump flow.
Once the desired fan speed is reached, the pressure cutoff spool will meter the flow of supply oil to the actuator piston and from the actuator piston. The adjustment of the cutoff spool can be adjusted for any maximum flow.
The cutoff spool is similar to a relief valve. If the motor would lock up, the cutoff spool would destroke the pump to a minimum angle. Then, the pump would produce minimum flow.
Reference: For information about the hydraulic fan pump, refer to the Service Manual module Systems Operation and Testing and Adjusting, "Piston Pump (Hydraulic Fan)" for the machine that is being serviced.
Reference: For information about the hydraulic fan motor, refer to the Service Manual module Systems Operation and Testing and Adjusting, "Piston Motor (Hydraulic Fan)" for the machine that is being serviced.
Reference: For information about adjusting the speed of the hydraulic fan system, refer to the Service Manual module Systems Operation and Testing and Adjusting, "Hydraulic Fan Speed - Test and Adjust" for the machine that is being serviced.
Electrical Control
In the demand fan system, the speed of the fan and the output of the hydraulic fan pump is directly controlled by the engine ECM through the solenoid valve. The engine ECM interprets signals from the four sensors on the machine. Then, the engine ECM sends a proportional amount of current to the solenoid valve.
The following sensors report directly to the engine ECM.
- Air intake temperature
- Hydraulic oil temperature
- Engine coolant
The sensor for the air intake temperature is a passive sensor that is used to measure temperature. The sensor sends an analog signal to the engine ECM. The analog signal will increase in voltage as the temperature of the air increases. The signal is carried to contact J2-35 to the engine ECM by wire G853-OR. The sensor returns to the engine ECM contact J2-18 through wire G833-PK.
The hydraulic oil temperature sensor is used for the measurement of liquid temperatures. The sensor sends an analog output to the engine ECM. The analog signal will increase in voltage as the temperature of the oil increases. The signal is carried to contact J1-17 of the engine ECM by wire 442-GY. The sensor receives the voltage from contact J1-2 through wire G879-OR and the sensor returns to the engine ECM contact J1-3 through wire J843-PU.
The engine coolant temperature sensor is a passive sensor that is used to measure the temperatures of liquids. The sensor sends an analog signal to the engine ECM. The analog signal will increase in voltage as the temperature of the engine coolant increases. The signal is carried to contact J2-32 to the engine ECM by wire 995-BU. The sensor returns to the engine ECM contact J2-18 through wire G833-PK.
The transmission oil temperature sensor is a sensor that measures the temperature of liquids. The sensor has a pulse width modulated signal that sends a square wave output. The duty cycle of the output will increase as the temperature increases. The transmission oil temperature sensor sends an output to power train ECM (7). Power train ECM (7) sends the information about the transmission oil temperature to engine ECM (12) by way of the Cat data link (10) .
The signal from the transmission oil temperature sensor is carried to contact J2-18 of the power train ECM by wire K997-OR. The sensor receives the voltage from contact J2-12 through wire 709-OR and the sensor returns to the power train ECM contact J1-15, J1-16 through wire 962-OR.
When the engine is started, the hydraulic fan pump will be instructed to run at minimum fan speed. The following conditions must be met, in order to run the fan system at minimum fan speed.
- The air intake temperature is below 49 °C (120 °F).
- The transmission oil temperature is below 93 °C (200 °F).
- The hydraulic oil temperature is below 90 °C (195 °F).
- The engine coolant temperature is below 89 °C (192 °F).
As one of the sensors reads a temperature that is above the key target temperature, the engine ECM interprets a demand for more cooling. The engine ECM starts sending a reduced amount of current to the solenoid valve. The solenoid valve will move proportionally, toward the de-energized direction.
As one of the sensors read a continuous increase in temperature, the engine ECM will continue to reduce the amount of current to the solenoid valve. When the output pressure from the fan pump is greater than the adjusted pressure of the cutoff spool, the hydraulic pump will go into high pressure cutoff. At this time, the speed of the hydraulic fan motor will no longer increase. The hydraulic fan system is at maximum air flow.