The radiator is designed to cool the 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 cooler can be installed in the cooling system. An oil cooler serves to cool the oil in the lubrication system.
The exhaust gas recirculation cooler cools the exhaust gases, thereby reducing the combustion temperature of the air-fuel mixture and the formation of nitrogen oxides. The exhaust gas cooler is operated by an additional coolant circulation pump included in the cooling system.
The heat exchanger of the heater performs a 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.
An expansion tank is installed to compensate changes in coolant volume due to temperature in the system. The system is usually filled with coolant through an expansion tank.
The circulation of the coolant in the system is provided by a centrifugal pump. In everyday life, a centrifugal pump is called a pump. A centrifugal pump can have a different drive:
gear, belt, etc. On some turbocharged engines, an additional coolant circulation pump is installed to cool the charge air and the turbocharger, which is connected by the engine control unit.
The thermostat is designed to regulate the amount of coolant passing through the radiator, which ensures the optimal temperature in the system. The thermostat is installed in the pipe between the radiator and the engine «cooling jacket».
Powerful engines are fitted with an electrically heated thermostat that provides two-stage coolant temperature control. For this, the thermostat has three operating positions: closed, partially open and fully open. When the engine is fully loaded, the electric heating thermostat opens it completely. In this case, the temperature of the coolant decreases to 90°C, the propensity of the engine to detonate decreases. In other cases, the coolant temperature is maintained within 105°C.
The radiator fan serves to increase the intensity of cooling the liquid in the radiator.
The fan can have a different drive:
-
Mechanical (permanent connection with the engine crankshaft);
-
Electric (controlled electric motor);
-
Hydraulic (fluid coupling).
The most widespread is the electric fan drive, which provides ample opportunities for regulation.
Typical cooling system controls are a coolant temperature sensor, an electronic control unit and various actuators.
The coolant temperature sensor records the value of the monitored parameter and converts it into an electrical signal. To expand the functions of the cooling system (cooling the exhaust gases in the exhaust gas recirculation system, regulating the fan operation, etc.), an additional coolant temperature sensor is installed at the radiator outlet.
The signals from the sensor are received by the electronic control unit and converted into control actions on the actuators. As a rule, an engine control unit with the appropriate installed software is used.
The following actuators can be used in the control system: thermostat heater, auxiliary coolant pump relay, radiator fan control unit, engine cooling relay after stop.
How the cooling system works
The cooling system is operated 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 conditions for switching on and the 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. This cools the engine and heats up the coolant. 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 the engine is started, 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 the radiator, where it is cooled by the counterflow of air. If necessary, the liquid is cooled by an air flow from the fan.
After cooling, the liquid is returned to the «cooling jacket» of the engine. During engine operation, the coolant cycle is repeated many times.
On turbocharged vehicles, 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.
