Fault analysis of silicone oil fan clutch

To maintain the optimal operating temperature of a diesel engine, fan control of the cooling system is essential. Currently, most heavy-duty trucks in China use silicone oil clutch fans, and cardholders may inevitably encounter problems such as fan failure during driving. At this time, many cardholders choose to lock the fan clutch. This is definitely not feasible.

 

The function of silicone oil fan clutch

Due to changes in environmental conditions and operating conditions, the thermal condition of the engine changes at all times. Therefore, the cooling intensity of the engine must be adjusted at all times. For example, in summer, when the engine operates at low speeds and high loads, and the temperature of the coolant is high, the fan should rotate at high speeds to increase the cooling air volume and enhance heat dissipation capacity; In the cold winter, it becomes meaningless for the fan to continue working when the coolant temperature is low. Not only does it consume engine power in vain, but it also generates a lot of noise.

 

If the temperature is below 10 degrees Celsius for more than 100 days, the actual engine cooling fan will be useless and the fuel consumed will be a very serious waste. This also explains why the clutch cannot be locked.

 

The principle of silicone oil fan clutch

Unlike ordinary rigid fans, the silicone oil fan clutch uses silicone oil as the medium and utilizes silicone oil shear viscosity to transmit torque.

 

The space between the front cover of the fan clutch and the driven plate is an oil storage chamber, where high viscosity silicone oil is stored.

 

The key sensing component is the spiral bimetallic sheet temperature sensor on the front cover, which deforms due to heat to control the valve plate and control the silicone oil to enter the working chamber to engage the drive shaft and fan.

 

When the temperature is low, the control valve does not open, and the silicone oil in the oil storage chamber cannot flow into the working chamber at this time. There is no silicone oil in the working chamber, the torque on the driving plate cannot be transmitted to the driven plate, and the clutch is in a disengaged state.

 

When the engine load increases and the coolant temperature increases, the high-temperature airflow blows onto the bimetallic temperature sensor, causing the bimetallic plate to deform and deflect the valve plate transmission pin and control valve plate by an angle. After the airflow temperature exceeds a certain temperature, the oil inlet hole is opened, and the silicone oil in the oil storage chamber enters the working chamber through this hole. The shear stress of silicone oil transmits the torque on the active plate to the clutch housing, driving the fan to rotate at high speed.

 

Frequent fault analysis

1. The spiral bimetallic plate temperature sensor is broken, causing the fan to not rotate.

2. The fatigue failure of the spiral bimetallic plate temperature sensor results in excessive temperature sensing conditions, which prevents the fan from working in a timely manner and affects engine performance.

3. The sealing of the oil storage chamber and working chamber is not tight, and the loss of silicone oil affects torque transmission.

 

In response to the above issues, some people choose to lock the fan clutch to solve the problem of high engine temperature.

 

Firstly, a locked fan clutch will consume a large amount of power. It is understood that a rigidly connected cooling fan requires 3-5% of the engine's power, resulting in astonishing fuel consumption.

 

Secondly, silicone oil can have a certain buffering effect.

 

With the progress of science and technology, the fan design of the cooling system has also undergone great changes, from the earliest rigid fan, to the silicone oil clutch fan, to the advanced electromagnetic clutch fan and electronic silicone oil clutch fan.

 

1. Rigid fan

The rigidly connected fan is directly affected by the engine speed. When the engine is running at low speeds, the cooling system temperature is forced to dissipate heat, causing the engine temperature to be too low and making it difficult for the engine to warm up in winter.

 

2. Silicone clutch fan

Silicone oil fan uses silicone oil as the medium, utilizes the high viscosity characteristics of silicone oil to transmit torque, and achieves temperature controlled operation of the fan through a dual temperature sensing metal deformation structure "coupler". The fan speed is controlled by temperature, avoiding useless operation at low temperatures. But this is only a simulated operation, and it is difficult to achieve accurate constant temperature of the cooling system, with ups and downs.

 

3. Electromagnetic clutch fan

The electromagnetic clutch fan can accurately control the fan speed through the control switch, intelligent control unit or engine ECU communication to further control the cooling system temperature and achieve two-stage or three-stage speed regulation. At present, the engine products of Heavy Truck and Weichai are equipped with this system.

 

4. Electronic silicone clutch fan

The electronic controlled clutch of the electronic silicone oil clutch fan is different from the traditional bimetallic temperature control mode. By directly reading the engine control module ECU signal, the internal solenoid valve of the fan clutch controls the speed of the cooling fan based on the information provided by temperature sensors in various parts of the engine. In order to achieve a more accurate and rapid response.

 

The engine is the core component of a truck, and the fan, as a cooling system, plays a crucial role in the efficiency of the engine. Do not lock it up because it is damaged.