The function of engine cooling fan is to enhance the air flow rate and flow rate through the radiator, so as to improve the cooling effect of the radiator. As an important part of the engine cooling system, the work of the fan not only directly affects the heat dissipation efficiency of the radiator, but also affects the normal use and reliability of the engine. This paper gives a brief introduction to the working principle and troubleshooting of common fan types of engines.

Ordinary cooling fan

The fan is located between the radiator and the body, mounted on the same shaft as the water pump, and driven by a pulley on the crankshaft. The fan is connected with the belt wheel hub with bolts, and the belt wheel of engine crankshaft drives the fan to rotate directly or indirectly.

The tightness of each belt should be adjusted according to regulations. Fan belt tight through loose, causing the fan pulley speed is reduced, the tank heat dissipating capacity is abate, make diesel engine work temperature, at the same time reduce the generator output current or unstable, but the fan belt tightness is not the bigger the better, fan belt too tight will make bearing load is too big, wear, power consumption increases, at the same time also can make water pump shaft bending, belt stretching deformation, shorten service life. Therefore, the fan belt should be kept properly tight and adjusted when necessary. Check the tightness of the belt method: with finger or ruler to 30 ~ 50 N pressure in the middle of the belt, belt down 10 ~ 20 mm is appropriate. Some engines have two belts, others three or four. Each belt gear shall be on the same plane and shall not be twisted when installed. If the belt is seriously worn or broken, it should be replaced in time. If the fan belt is two, the replacement must be replaced at the same time, so as to avoid its tension, uneven force, causing fault.

2 clutch fan

Compared with the ordinary fan, the clutch fan is equipped with a fan clutch between the belt pulley and the hub of the blade, which can adjust the working state of the fan through the separation and engagement of the clutch. This not only ensures the normal operating temperature of the engine, but also reduces the power loss and fuel consumption of the engine. Common clutch fan has electromagnetic clutch fan and silicon oil clutch fan.

The electromagnetic fan clutch, when the coolant temperature reaches the specified value, the coolant temperature sensor switch or air temperature sensor switch automatically switch on the circuit, the clutch coil is energized to form a closed magnetic circuit to generate magnetic tension, so that the armature and pulley joint, fan work; When the coolant temperature drops, the sensor switch is disconnected, the armature is quickly reset under the action of the diaphragm spring, the clutch is separated, and the fan stops working.

The silicon oil clutch fan is in a closed state when the engine temperature is high. The fan works to reduce the temperature of the radiator. When the engine temperature is low, the fan clutch automatically disengages and the fan does not turn, saving engine power and raising the cooling water temperature.

Fan rotation does not indicate whether the fan clutch is malfunctioning, because both the malfunctioning and normal fan clutch will follow the pump belt pulley when it is in the state of disengagement. You can tell if the fan clutch is working by listening to the sound of the fan. A normal fan clutch makes a sound that works normally when the engine's water temperature is higher than 86 ° c, while a malfunctioning fan clutch makes a much quieter sound. When the fan clutch fails, when the engine water temperature is high, the fan does not turn, then it is necessary to turn off the engine, loosen the nut, insert the locking plate into the pin hole of the drive shaft, so that the fan and the drive shaft are fixed, do not use the fan clutch, so that the fan is forced to turn; When there is an opportunity to repair the fan clutch, then restore the fan clutch automatic clutch function.

3 electric fan

Electric fan working principle, this kind of fan is driven by its own fan motor. The motor's circuit switch is controlled by a fan sensor (temperature control switch) mounted in the radiator launching chamber. When the radiator water temperature is above 86-90 ℃, the temperature control switch is connected to the fan motor circuit, making the fan rotate to accelerate the radiator cooling. When the radiator water temperature drops to below 81-85 ℃, the fan sensor is disconnected, the fan motor circuit is broken, and the fan stops rotating. Maintenance of common faults:

3.1 the coolant temperature is too high at idle speed and normal at low speed

The most common cause of excessive cooling fluid temperature at idle and normal temperature at low speed is insufficient air volume of cooling fan. Check from the following aspects :(1) whether the diameter of the fan blade conforms to the manufacturer's regulations; (2) whether the Angle of the fan blade and the number of blades conform to the manufacturer's regulations; (3) whether the distance between the fan blade and the radiator is appropriate. Under normal circumstances, the fan blade should be about 1/3 enclosed in the fan cover.

3.2 observe the coolant temperature when the radiator fan rotates

Note the temperature of the coolant as the radiator fan rotates. Under normal circumstances, when the engine coolant temperature of some models is about 95℃, the electrically controlled fan starts to rotate at a low speed, and when the engine coolant temperature is about 105℃, the electrically controlled fan starts to rotate at a high speed. When the engine coolant temperature of some models is about 106℃, the electrically controlled fan starts to rotate at a low speed. When the engine coolant temperature is about 110℃, the electrically controlled fan starts to rotate at a high speed. If the rotation of the electrically controlled fan is abnormal, the specific reason should be further investigated. When the coolant temperature sensor transmits a signal that the coolant temperature reaches 106℃ to the control unit, the control unit provides grounding for the low-speed fan relay. The current passes through the closed contact of the fuse and relay, and supplies power to the electrically controlled fans on both sides. The two electrically controlled fans form a series and start to rotate at a low speed. When the coolant temperature sensor transmits a signal to the control unit that the coolant temperature reaches 110℃, the control unit provides grounding for the high-speed fan relay. After a 3s delay, the relay contact of the high-speed fan control circuit closes, and the two electrically controlled fans form a series again and start high-speed rotation.

3.3 the importance of keeping the appearance of condenser and radiator clean

In front of the engine radiator is air conditioning condenser, radiator and condenser is located in the forefront of the engine room, the road is liable to be sundry jam, cause air liquidity is poor, thus increasing the electric fan work load, the electric fan start instantaneous electric current too big, and easy to burn poor contact electric fan wire terminals, and electric fan wire terminals after burning can make electric fan starting resistance increases, the startup time lag, causes the engine coolant temperature is too high, serious when still can burn out the fuse. Therefore, compressed air should be applied to clean the radiator and condenser of the engine before summer to restore good ventilation.

3.4 signal misalignment of the temperature sensor of ktir coolant

The self-test of engine coolant temperature sensor by the control unit self-diagnosis system is limited to voltage and time limit. As for the voltage, the output voltage signal of the coolant temperature sensor only needs to be within the range of 0.1 ~ 4.8v, and the test can pass. The accuracy is not within the monitoring range of the self-diagnosis system. The so-called time limit is that when the engine works for 10 minutes, the output voltage signal of the coolant temperature sensor reflects that the coolant temperature is greater than 60℃, and the test can pass. When the engine coolant temperature reaches 106℃, the electrically controlled fan should start to rotate at a low speed. If the actual coolant temperature has reached or even exceeded 106℃, and the output voltage signal of the coolant temperature sensor reflects that the coolant temperature is below 100℃, the electrically controlled fan cannot rotate and the engine coolant temperature will be too high. In order to test whether the output voltage signal of the coolant temperature sensor is accurate, except that its resistance value is consistent with the manufacturer's regulation at a specified temperature. Can also be coolant thermometer (partial engine signal from the coolant temperature sensor plug, another part of the signal of engine coolant temperature sensor), data flow (signal from the coolant temperature sensor), and the infrared thermometer on the radiator inlet pipe (the actual engine cooling fluid temperature) temperature detection, one of the highest measurement accuracy is the infrared thermometer.