The Working Principle Of Automobile Engine Cooling System

1. Working principle of forced circulation and thermostat

Working principle of forced circulation of cooling water
As shown in FIG. 6, when the engine is working, it drives the water pump to work. After the water pump pressurizes the coolant from the radiator outlet pipe, it is forced into the channel inside the engine cylinder.
As the water pump is in a continuous working state, the coolant is continuously squeezed into the cylinder block, and the water pressure is increased and conveyed to the radiator outlet pipe through the thermostat.
In this forced circulation system, the amount of water pumped by the pump depends on the thermostat connected in series in the water pipe. The pump shown in Figure 7 is installed in the inlet channel, and the thermostat is installed in the outlet channel.
The pump pumps water from the radiator to the cylinder channel, and the thermostat controls the size of the outlet flow.
Figure 6 and Figure 7 show the simplest arrangement common in cars. The throttle is installed at the front end of the water pump and controls the size of the inlet water flow.

2.The principle of temperature regulation

When the engine is working, the pump is driven by the water pump transmission system to rotate the cooling hydraulic pressure into the engine, and the heat is brought to the radiator in the circulating flow process of the coolant, and the heat is emitted to the atmosphere by the radiator.

As shown in FIG. 8, the function of the thermostat is to make the engine warm up to the mechanical temperature required for normal operation in a short period of time by controlling the size of the closed channels.
When the cooler starts, the thermostat closes the flow circulation channel leading to the radiator. At this time, only the small water flow channel or bypass water flow is available on the thermostat. The purpose is to limit the circulation amount of cooling water, shorten the preheating time and prevent the phenomenon of too long preheating time.
With the extension of engine preheating time, when the temperature of the coolant rises, the thermostat begins to open the large water circulation channel and increase the forced circulating water flow to meet the demand of the coolant amount due to the temperature rise of the engine.
The opening channel section of the thermostat depends on the water temperature.
The higher the water temperature, the larger the section of the channel opened by the thermostat, and the greater the circulation of cooling water.
At the same time, the thermostat can also reduce the section of channel opening in time according to the gradual drop of cooling water temperature.
Therefore, the thermostat has two major functions. One is to close the strong circulating water flow, so that the engine quickly preheats up and warms up.
Second, adjust the size of forced circulation water flow timely and accurately.

3.Radiator pressure relief and supplementary flow principle

When the engine is working, the water temperature in the radiator is rising, and the radiator and the whole inlet and outlet channel are sealed under the action of the radiator cover, so when the water temperature rises, the pressure in the system is also rising with the temperature.
In order to prevent excessive internal pressure from damaging system parts, a safety valve (discharge valve) and a refill valve (refill valve) are arranged on the radiator cover.
As shown in FIG. 9, when the pressure in the radiator is too high, the safety valve in the radiator cover opens, and the high-pressure water vapor in the radiator flows to the secondary liquid storage tank through the pipe.
When the pressure in the radiator drops, the relief valve closes.
After the safety valve is closed, because the water pump is working continuously, negative pressure is formed in the radiator and the supplementary flow valve (recharging valve) is opened, and the coolant in the deputy liquid storage box is added to the radiator to prevent water shortage and pump back pressure increase in the radiator.

4.Working principle of fan motor control

Fan motor system is shown in Figure 10, which is mainly composed of fan, DC motor, thermal switch type water temperature sensor and power supply.
The fan suit is at the rear end of the radiator, and the air is pumped inward when working.
Thermal switch type water temperature sensor installed in the main channel of the radiator, is a temperature switch controlled by the water temperature, its working characteristic is on or off the internal circuit.
There are two ways to control the input power of the air-cooled motor. One is to deliver the working power to the motor through the output end of the ignition switch, and the other is directly connected to the total power line of the battery.
The latter can be connected in the engine when the water temperature is high, that is, to close the ignition switch, the fan motor can still work, until the water temperature drops, by the thermal temperature switch to cut off the motor grounding circuit.
The former ignition switch and thermal switch series control the motor line, ignition on and off, the motor can not work.
The on-off of the working circuit of the motor system is directly controlled by the thermal switch. When the water temperature in the radiator reaches the internal on-off temperature of the thermal switch, the on-off of the thermal switch makes the motor work.
When the water temperature drops to the internal temperature of the thermal switch, the circuit will be cut off automatically.

5.Water temperature indicator principle

The water temperature indicator system is shown in FIG. 11, in which the top three small pictures are the physical water temperature indicator, the internal structure of the water temperature indicator (electromagnetic type), thermistor, and the schematic diagram in the lower half.
Its working principle is: the engine cooling water temperature too low, the inside of the thermistor resistance is very big, because the L1 and thermistor resistance in a circuit is more than the value of L2, L2 so at this time through the current is large, the core of the magnetic field generated the metal plate to the right of the bottom of the clock shift rotation, the clock has swing to the left to the low temperature area.
As the temperature of cooling water continues to rise, the resistance value inside the thermal resistance continues to decrease, and the Ll coil gradually begins to have current flow from no current, so that the magnetic energy generated by L2 core is constantly enhanced, and the disk at the lower end of the table shaft is constantly sucked to the left, and the needle moves to the right, indicating the temperature is also rising.
When the water temperature is too high, the resistance of the thermistor decreases until the minimum resistance, at this time because the resistance of L2 is much greater than L1, L1 current enhancement and L2 almost no current, so the needle is L2 core suction to the left high temperature zone.
After the cooling water temperature of the engine drops, the needle also constantly moves to the left, and points to the low temperature area or the normal working temperature area.

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