AC Fan Control The cooling fan speed control by the target coolant temperature control and fan speed control of two parts.
1.1 Target coolant temperature control strategy
The characteristic curves of the two target coolant temperatures are stored in the AC Fan Control unit.
The first target coolant temperature characteristic graph reflects the relationship between the target coolant temperature and the engine load (intake air volume) and the engine speed, where the engine load is a major factor affecting the target coolant temperature. The target coolant temperature must be consistent with the engine load, and the appropriate coolant temperature can improve engine performance. (95 ℃ ~ 105 ℃) is conducive to the engine to improve performance, reduce fuel consumption and reduce emissions of harmful substances; full load when the temperature is lower (85 ℃ ~ 95 ℃), in order to reduce the heating effect of the intake , Thereby increasing the power output, which will help improve the power.
The second characteristic graph reflects the relationship between the target coolant temperature and the vehicle speed and ambient temperature. Using this characteristic curve, the difference between the temperature of the coolant detected by the coolant temperature sensor and the temperature of the coolant at the engine water jacket can be effectively corrected. In high temperature environments (such as tropical deserts) at low speeds and at high temperatures in low temperature environments (eg northeast of the winter), the temperature of the coolant temperature sensor is the same, but the temperature of the engine water jacket and the engine compartment is different, The temperature of the coolant temperature sensor at low temperature and high speed is much lower than the actual operating temperature of the engine, while the high temperature and low speed travel is just the opposite. Therefore, in the calculation of the target coolant temperature to use the detected speed and the external temperature of the appropriate correction, in general, the higher the speed and the lower the ambient temperature, the target coolant temperature should be appropriate to reduce 2 ℃ ~ 5 ℃.
The AC Fan Control unit compares the two characteristic graphs and takes the lowest value to control the operation of the cooling fan. When the cooling coolant temperature of the engine exceeds the target temperature, the cooling fan begins to operate. Under normal circumstances, in the normal working conditions when the target coolant temperature is about 93 ℃, that is, when the coolant temperature reaches 93 ℃ after the cooling fan began to work.
1.2 Cooling fan speed control strategy
The purpose of the cooling fan speed control is to make the actual coolant temperature closer to the target coolant temperature. As with the target coolant temperature, two cooling fan speed characteristics are also stored in the AC Fan Control unit.
Cooling fan characteristic curve 1 reflects the relationship between the cooling fan speed and the vehicle speed and the target coolant temperature. The lower the speed, the lower the natural wind, the cooling fan speed will be higher accordingly; the other hand, the higher the speed of the natural wind cooling effect is better, the corresponding cooling fan speed lower, generally when the speed of more than 100 km / h, The cooling fan does not need to run.
The cooling fan characteristic curve 2 reflects the relationship between the cooling fan speed and the difference between the two coolant temperature sensor detection data and the target coolant temperature. When the engine outlet coolant temperature sensor detects the coolant temperature value in the normal range, but the radiator outlet coolant temperature sensor detects the coolant temperature is low, indicating that the radiator temperature is not high, the role of cooling fan work is not large, So the cooling fan speed should be reduced; when the coolant temperature of the engine outlet coolant detects the coolant temperature is higher (already higher than the normal range), but if the radiator outlet coolant temperature sensor detects the coolant temperature is low, It shows that the thermostat is faulty, this time to protect the engine and need to control the cooling fan high-speed operation.
In addition, the cooling fan operation and speed and speed according to the needs of air conditioning systems to control.
The AC Fan Control unit calculates the optimum cooling fan operating speed based on the internal coolant temperature characteristic curve and the cooling fan speed characteristic curve according to the signals provided by the respective sensors and converts the cooling fan speed data into duty ratio data, and then The control unit emits the PWM signal to the cooling fan control unit, and the cooling fan control unit controls the two fans to operate at a certain speed according to the received duty ratio of the AC Fan Control unit.
Normally, the duty ratio control signal sent by the AC Fan Control unit to the cooling fan control unit is 10% to 90%. When the cooling fan control unit receives the duty ratio signal of this interval, it will vary according to the duty cycle , Control the cooling fan speed.
In order to prevent the PWM signal line generated by the AC Fan Control unit from being shorted to ground or power, when the cooling fan control unit detects that the PWM signal is 0 V or 12 V, the cooling fan control unit controls the fan to rotate at the highest speed.
The operating power source of the cooling fan control unit is supplied from the power supply relay (J271) of the AC Fan Control unit. The working power of the cooling fan is provided by No. 30 FireWire. When the ignition switch is turned off, the AC Fan Control unit can still work, when the AC Fan Control unit detects the coolant temperature is too high and need to cool down, to the cooling fan control unit issued PWM signal, cooling fan control unit can continue to work.