The function of the cooling system is to keep the engine within the proper temperature range under all operating conditions. The cooling system not only prevents the engine from overheating, but also prevents the engine from being too cold in winter. After the engine is cold started, the cooling system must also ensure that the engine heats up quickly and reaches the normal operating temperature as soon as possible.
The dangers of engine overheating
(1) Reduce the inflation efficiency and reduce the engine power;
(2) The tendency of deflagration increases, causing early damage to parts due to additional impact loads;
(3) The normal clearance of the moving parts is destroyed, the movement is blocked, the wear is intensified, and even damaged;
(4) The lubrication condition deteriorates, which intensifies the friction and wear of parts;
(5) The mechanical properties of the parts are reduced, resulting in deformation or damage.
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The dangers of engine overcooling
(1) The temperature of the mixed gas (or air) entering the cylinder is too low, and the quality of the combustible mixed gas is poor, which makes ignition difficult or combustion slow, resulting in a decrease in engine power and an increase in fuel consumption;
(2) The water vapor in the combustion product is easy to condense into water and form acids with acid gas, which aggravates the corrosion effect on the body and parts;
(3) The unvaporized fuel washes and dilutes the oil film on the surface of the parts (cylinder wall, piston, piston ring, etc.), which intensifies the wear of the parts.
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How the engine is cooled
Depending on the cooling medium, there are two cooling methods for the engine: air-cooled and water-cooled.
Most engines are now water-cooled, and air-cooled is only used on some special vehicles, some construction machinery and motorcycles. So today I will only talk about the water cooling system.
The water cooling system of the automobile engine is a forced circulation water cooling system, that is, the water pump is used to increase the pressure of the coolant, and the coolant is forced to circulate in the engine. Such systems include water pumps, radiators, cooling fans, thermostats, compensation buckets, water jackets in the engine block and cylinder heads, and other add-ons.
How the engine cooling system works
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The circulating water cooling system uses a water pump to pressurize the coolant in the system to make it flow in the water jacket, the cooling water absorbs heat from the cylinder wall, the temperature rises, the hot water flows upward into the cylinder head, and then flows out from the cylinder head and into the radiator. Due to the strong suction of the fan, the air flows through the radiator from front to back at high speed, constantly taking away the heat of the water flowing through the radiator.
The cooled water is re-pumped from the bottom of the radiator into the water jacket by the water pump. Water circulates continuously in the cooling system. In order to control the cooling water temperature, the cooling system is equipped with cooling intensity adjustment devices, such as shutters, thermostats and fan clutches.
heat sink
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The radiator is what we often call the water tank, which is divided into two types: vertical flow type and cross flow type. Most new cars feature cross-flow radiators, which allow for a lower bonnet profile, which helps improve aerodynamics at the front end.
The radiator cover is installed on the water inlet, and there is a steam-air valve on it, so that the pressure of the cooling system is higher than the atmospheric pressure, and the boiling point of the cooling water is increased.
The steam valve is generally opened when the pressure inside the radiator reaches 126kPa~137kPa, and part of the water vapor is discharged into the atmosphere through the vent pipe to avoid damage to the radiator.
When the air pressure in the radiator drops to 99kPa~87kPa, the air valve opens, and the radiator communicates with the atmosphere to prevent the radiator core from being damaged by the atmosphere.
Expansion tank
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Expansion tanks are mostly made of translucent materials (such as plastic). The upper part of the expansion tank is connected to the water filling pipe of the water tank with a thinner hose, and the bottom is connected to the water inlet side of the water pump through a water pipe, usually slightly higher than the radiator.
Turn the cooling system into a permanent closed system, avoid air entry, separate water and steam in the cooling system, keep the pressure in the system stable, and increase the water pumping capacity of the water pump.
Supplementary coolant: there are two engraved lines on the expansion tank, the coolant should be added to the upper engraved line (FULL), and when the liquid level drops to the lower engraved line (LOW), it should be replenished in time.
water pump
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The function of the water pump is to pressurize the coolant to ensure its circulation in the cooling system. Centrifugal water pumps are widely used in automobile engines now.
fan
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The function of the fan is to suck in air to pass through the radiator when the fan rotates, so as to enhance the heat dissipation capacity of the radiator and accelerate the cooling speed of the coolant. .
The water cooling system of many car engines uses electric fans, so the fan speed has nothing to do with the engine speed. In some electronically controlled systems, electric fans are controlled by a computer. When the engine is stopped, the electric fan will continue to rotate for a period of time due to the high water temperature in order to better dissipate heat for the engine.
As mentioned earlier, to ensure that the engine works at the optimum temperature without overheating or overcooling, it is necessary to automatically adjust the engine cooling intensity according to changes in operating conditions.
Cooling intensity adjustment methods: one is to change the air flow and velocity flowing through the radiator; the other is to change the flow and circulation route of the cooling liquid.
thermostat
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The function of the thermostat is to automatically change the flow rate and circulation route of the coolant according to the engine load and water temperature, so as to ensure that the engine works at a suitable temperature and reduce fuel consumption and wear of parts.
Large circulation of water cooling system
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The cooling water passes through the water pump-water jacket-thermostat-radiator, and then is pressed into the water jacket by the water pump. The water flow path is long and the heat dissipation intensity is high, which is called the large circulation of the water cooling system.
Small circulation of water cooling system
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The cooling water passes through the water pump-water jacket-thermostat and does not pass through the radiator, but is directly pressed into the water jacket by the water pump. The water flow path is short and the heat dissipation intensity is small, which is called the small circulation of the water cooling system.
