The cooling system is designed to cool engine parts heated as a result of its operation. On modern cars, the cooling system, in addition to the main function, performs a number of other functions, including:
Depending on the cooling method, the following types of cooling systems are distinguished: liquid (closed type), air (open type) and combined. In a liquid cooling system, heat from heated parts of the engine is removed by a fluid stream. The air system uses airflow for cooling. The combined system combines liquid and air systems.
On cars, the most widely used liquid cooling system. This system provides uniform and efficient cooling, and also has a lower noise level. Therefore, the device and principle of operation of the cooling system are considered on the example of a liquid cooling system.
The design of the cooling system of gasoline and diesel engines are similar. The engine cooling system includes many elements, including a radiator of a cooling liquid, an oil radiator, a heat exchanger of a heater, a radiator fan, a centrifugal pump, as well as an expansion tank and a thermostat. The cooling system includes an engine cooling jacket. To regulate the system, controls are used.
The radiator is designed to cool a heated coolant with an air stream. To increase heat transfer, the radiator has a special tubular device.
Along with the main radiator, an oil cooler and an exhaust gas recirculation radiator can be installed in the cooling system. The oil cooler is used to cool the oil in the lubrication system.
The exhaust gas recirculation radiator cools the exhaust gases, thereby lowering the temperature of combustion of the fuel-air mixture and the formation of nitrogen oxides. The operation of the exhaust gas radiator is provided by an additional coolant circulation pump included in the cooling system.
The heat exchanger of the heater performs the function opposite to the radiator of the cooling system. The heat exchanger heats the air passing through it. For efficient operation, the heater heat exchanger is installed directly at the outlet of the heated coolant from the engine.
To compensate for changes in the volume of the coolant due to temperature, an expansion tank is installed in the system. Filling the system with coolant is usually done through an expansion tank.
Coolant circulation in the system is provided by a centrifugal pump. In everyday life, a centrifugal pump is called a pump. The centrifugal pump can have a different drive: gear, belt, etc. On some engines equipped with a turbocharger, an additional coolant circulation pump is installed to connect the charge air and the turbocharger, which is connected by the engine control unit.
The thermostat is designed to adjust the amount of coolant passing through the radiator, thereby ensuring optimal temperature conditions in the system. The thermostat is installed in the pipe between the radiator and the “cooling jacket” of the engine.
On powerful engines, a thermostat with electric heating is installed, which provides two-stage temperature control of the coolant. To do this, the design of the thermostat has three operating positions: closed, partially open and fully open. When the engine is fully loaded with the electric heating of the thermostat, it is fully opened. In this case, the temperature of the coolant decreases to 90 ° C, the propensity of the engine to detonate is reduced. In other cases, the coolant temperature is maintained within 105 ° C.
The radiator fan is used to increase the intensity of cooling the liquid in the radiator. The fan can have a different drive:
The most widely used electric fan drive, providing ample opportunity for regulation.
Typical cooling system controls are a coolant temperature sensor, an electronic control unit, and various actuators.
The coolant temperature sensor captures the value of the monitored parameter and converts it into an electrical signal. To expand the functions of the cooling system (cooling the exhaust gas in the exhaust gas recirculation system, regulating the operation of the fan, etc.), an additional coolant temperature sensor is installed at the radiator output.
The signals from the sensor are received by the electronic control unit and convert them into control actions on the actuators. As a rule, an engine control unit with appropriate software installed is used.
The following actuators can be used in the operation of the control system: thermostat heater, relay for the additional coolant pump, radiator fan control unit, engine cooling relay after stopping.
The operation of the cooling system is provided by the engine management system. In modern engines, the operation algorithm is implemented on the basis of a mathematical model that takes into account various parameters (coolant temperature, oil temperature, outside temperature, etc.) and sets the optimal switching conditions and operating time of structural elements.
The coolant in the system has forced circulation, which is provided by a centrifugal pump. The movement of fluid is carried out through the “cooling jacket” of the engine. In this case, the engine is cooled and the coolant is heated. The direction of fluid movement in the “cooling jacket” can be longitudinal (from the first cylinder to the last) or transverse (from the exhaust manifold to the intake).
Depending on the temperature, the liquid circulates in a small or large circle. When starting the engine, the engine itself and the coolant in it are cold. To accelerate engine warm-up, the coolant moves in a small circle, bypassing the radiator. The thermostat is closed.
As the coolant heats up, the thermostat opens and the coolant moves in a large circle – through the radiator. The heated liquid passes through a radiator, where it is cooled by an oncoming air stream. If necessary, the liquid is cooled by a stream of air from the fan.
After cooling, the liquid enters the engine cooling jacket again. During engine operation, the coolant cycle is repeated many times.
On cars with turbocharging, a dual-circuit cooling system can be used, in which one circuit is responsible for cooling the engine, the other for cooling the charge air.
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