824H Wheel Dozer and 825H Soil Compactor
The hydraulic fan system is used to meet the cooling requirements of the machine. The hydraulic fan system reduces the horsepower that is used by the hydraulic fan system in a cooler condition or a light work application. The hydraulic fan system will control the fan speed through the use of a variable displacement piston pump which directly drives a fixed displacement hydraulic motor. The engine control module (ECM) takes inputs from four different sensors on the machine. The ECM interrupts the requirements for cooling the machine in the environment that the machine is being operated.
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| Illustration 1 | g00798352 |
Schematic for the Hydraulic Fan System (1) Check valve (hydraulic oil cooler bypass). (2) Oil cooler. (3) Radiator. (4) Hydraulic fan motor. (5) Filter. (6) Electrohydraulic control valve. (7) Pressure and flow compensator valve. (8) Hydraulic piston pump. (9) Hydraulic tank. (10) Engine ECM. (11) Sensor for the transmission oil. (12) Sensor for the hydraulic sump. (13) Sensor for the engine coolant. (14) Sensor for the inlet manifold temperature. | |
Hydraulic piston pump (8) is mounted to the front housing of the engine on the right side of the machine. Hydraulic piston pump (8) draws oil from hydraulic oil tank (9) through the inlet of the fan pump. Pressurized oil then flows to fan drive motor (4). Fan drive motor (4) is located at the rear of the machine between the radiator (3) and the engine. Pressurized oil from fan drive pump (9) flows into the inlet of fan drive motor (4). The high flow of the hydraulic oil causes the fan drive motor to rotate the fan blades. The rotation of the fan forces cool air to flow through the cooling package.
After the hydraulic oil exits the fan drive motor (4), the oil flows through a hydraulic oil line to hydraulic oil cooler (2). 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 and check valve (hydraulic oil cooler bypass) (1) will open. Check valve (1) limits the maximum oil pressure in hydraulic oil cooler (2) to 450 ± 55 kPa (65 ± 8 psi). Case drain oil from piston pump (8) and the case drain from piston motor (4) flow through a hydraulic oil line to hydraulic oil tank (9). The oil from the case drain is filtered through a screen in hydraulic tank (9) .
When the temperature of the oil increases, and the pressure of the oil decreases, the force of the spring in check valve (1) for hydraulic oil cooler (2) is greater than the force of the oil pressure that is acting on the spring. This allows the check valve (1) to close. The hydraulic oil flows through hydraulic oil cooler (2), through hydraulic oil filter (5), and then into hydraulic oil tank (9) .
The hydraulic fan system controls the speed of the fan. The hydraulic fan system allows the speed of the fan to decrease in cool ambient temperature or in a light work application. The fan speed is controlled by the four temperature sensors (11), (12), (13), and (14). The sensors send data to engine ECM (10). Engine ECM (10) will interpret the data from the four sensors. Engine ECM (10) will send a change in current to electrohydraulic control valve (6). The change in current to the valve will change the flow of oil from electrohydraulic control valve (6) to the spools in pressure and flow compensator valve (7). The movement of the spool in the pressure and flow compensator valve will decrease the angle of the swashplate in the hydraulic fan pump. By changing the angle of the swashplate, the volume of oil from hydraulic pump (8) will decrease and the decrease in the angle of the swashplate will slow the flow of oil to hydraulic motor (4) .
Pressure and flow compensator valve (7) which controls the pump flow is mounted on top of fan drive pump (8). Pressure and flow compensator valve (7) contains a flow control spool and a pressure cutoff spool. The settings of both spools can be adjusted.
Reference: For information about adjusting the speed of the piston motor (hydraulic fan), refer to the Service Manual module Testing and Adjusting, "Hydraulic Fan Speed" for the machine that is being serviced.
Reference: For more information on the hydraulic fan pump, refer to the Service Manual module Systems Operation, "Piston Pump (Hydraulic Fan)" for the machine that is being serviced.
Reference: For more information on the hydraulic fan motor, refer to the Service Manual module Systems Operation, "Piston Motor (Hydraulic Fan)" for the machine that is being serviced.