Technical report on thermal management.

04-06-2019 - Reports

 

Thermal management

 

In this report, different temperature control systems generated by engine activity are explained, all of them part of the wide FAE product catalogue.



1. Introduction to thermal management
         1.2. Engine cooling
2. Thermostats: regulation of the flow of refrigerant
         2.1. Wax thermostat: the most used one at present
3. Temperature switches: fan management and anomaly alarm
         3.1. FAE alarm temperature switch
         3.2. FAE fan temperature switch
4. Control valves: heating of the interior of the passenger compartment
5. Temperature sensors: temperature control of the liquid coolant

 

The products encompassed by FAE in this group are:

 

1. INTRODUCTION TO THERMAL MANAGEMENT 


The very activity of an engine generates high operating temperatures that can reach up to 2000ºC in combustion and that can damage, or even melt, the materials of the engine.
A high temperature in the engine results in the expansion of materials that can cause seizure and deformation. Moreover, less than a quarter of the heat energy consumed in the internal combustion engine is transformed into useful force. The rest of the heat must be dispersed in order to avoid any part of the engine heating to the point that the proper functioning of the engine itself would be hindered. Thus, the cooling of an engine is essential for its proper functioning and durability.
EThe cooling system must carry away the heat produced by combustion and the internal friction of the engine and maintain an ideal constant operating temperature within the limits that allow the engine to be as efficient as possible without damaging the mechanics of it.

Besides, the cooling system should help to warm up the engine at its ignition, to secure the ideal operating temperature as soon as possible

In the image we can see the graph of the high temperatures in the internal combustion chamber can exceed 2000 º.


 
1.2. ENGINE COOLING

One of the most used cooling systems at present is water-cooled cooling system.
A circuit through hollow cavities in the engine allows water circulation, which mixed with coolant liquid and anti-freeze solution cools down the internal walls of the ducts, carrying heat away. The water leaves the engine to cool down thanks to the action of the radiator, then re-enters the engine and cools it down.

Due to the high temperatures and the high revolutions that cars currently reach, the water circulation through the engine must be very high. The faster the water circulates, the less flow will be necessary.
A centrifugal water pump is responsible for regulating the flow of water suitable for each situation. At higher revolutions of the engine, the greater the speed of water circulation through the system needs to be.
The water enters the engine through the lower part and passes through the hollow interior of the cylinder head and the combustion chamber, leaving through the upper part. From there, it goes directly to the radiator, which is a heat exchanger, where the water cools when exposed to cold air, thanks to the extensive cooling surface in its cell structure. The cooled water is sent back into the engine by the suction of the water pump.
The forced circulation system is capable of maintaining the water temperature stable at about 85-90ºC, since a sudden change in the temperature of the engine, either by cooling or heating, can cause expansion or contraction of engine materials.
The heat that is dissipated by the engine cooling system is also used for the heating of the passenger compartment. When the heating of a car is turned on, a small heat exchanger heats the air that will heat the cabin.                                                                                       



                                                                                                                                                        Scheme of the water cooling system.


 
 


 
2. THERMOSTAT: REGULATION OF THE REFRIGERANT FLOW

The thermostat or thermostatic valve controls that the operating temperature is between the ideal limits for the proper functioning of the engine. The valve is responsible for regulating the circulation of water through the circuit to maintain a stable engine temperature between 70ºC and 90ºC, ideal limits for proper functioning of an engine.
The operating temperature of an engine directly affects lubrication and feeding, as well as fuel consumption and, therefore, pollution.

At low operating temperatures the fuel mixture does not reach the required calorific value and its consumption increases. The oil is denser, which hinders internal movement. On the contrary, at high temperatures oil loses its lubricating properties and the engine materials suffer.

The thermostat is located at the outlet of the engine block, before the radiator. When water temperature is lower than expected, the thermostat remains closed, so that water does not circulate through the radiator and the engine is heated before. In fact, what causes the closing of the thermostat is the reduction in the efficiency of the cooling circuit, which reduces the circulation of the coolant liquid or even suppresses it and makes it circulate only inside the engine block.



                                                                                                     
                                                                                                                                                         Detail of the parts of a FAE wax thermostat.                 

 

This way, the engine warms up much faster when the engine is started, reducing the time it operates at low temperatures. The most used thermostat type today is the one known as a wax thermostat.

Typologies of FAE thermostats:

 

 FAE thermostat. Complete kits of FAE thermostats. FAE water flanges.




2.1. . THE WAX THERMOSTAT: THE MOST USED ONE AT PRESENT

The wax thermostat consists of a capsule with wax inside of it. With changes in temperature, the volume of the wax changes considerably. When heated, it expands, consequently pushing a rubber membrane attached to a rod and causing the capsule to move and open the thermostat, letting the water to circulate through the cooling system. When cooled, it contracts, consequently causing the capsule to return to its original position, due to the effect of the spring, and closing the valve again, thus preventing the circulation of water through the circuit.

For this system to work properly, the cooling system must be watertight, so that the boiling point of water rises above 100ºC, which favours cooling. Thus, maintaining the tightness of the sealed areas, such as the thermostat cover, is important.
The above explained process is how the valve keeps the operating temperature stable in the engine’s cooling system.

 
 
 
 
          
 
                                                                                    Functioning of an FAE wax thermostat.




3. TEMPERATURE SWITCHES: FAN MANAGEMENT AND ANOMALY ALARM

Engines incorporate a fan to help in the cooling, which, moved by the motor itself, generates a forced air circulation through the radiator, ensuring better cooling of the water, especially during slow driving and at idle speed.
Although its operation is not continuous, when the speed of the car is fast, the air entering through the front grid will be enough for cooling. In this case, the fan will remain off to minimize consumption and for a quieter circulation.
In cars with air conditioning, the fan also cools the condenser, in which case one or two more powerful fans are necessary.
To control the functioning of the radiator fan, or to warn the driver of an anomaly in the temperature of the motor, so-called temperature transmitters are used.
They are switches that, mounted in the cooling circuit in the radiator or close to it, act with variations of the temperature. Above a certain temperature limit, they trigger the opening or closing of electrical contacts.

There are two types of FAE temperature transmitters:





3.1. FAE alarm temperature switch

Alarm temperature switch refer to a system that informs the driver of an abnormal state of the engine temperature.

 
                                                                                                                                                      Dissection of a FAE alarm thermal contact.




3.2. FAE fan temperature switch

Connects/disconnects the fan of the radiator according to the desired temperature to achieve the optimum operating temperature of the engine.



 
                                                                                                                                                        Dissection of a FAE fan thermal contact.

 



4. CONTROL VALVE: HEATING OF THE INTERIOR OF THE PASSENGER COMPARTMENT


The FAE control valve is an electromechanical valve that controls the passage of fluid through a conduit. The control valve is moved by a solenoid coil, which generates the mechanical energy necessary for the valve to open or close the fluid passage.

As mentioned earlier, to heat a passenger compartment of a car, an engine cooling circuit is used as a heat source. The cooling fluid flows through a small heat exchanger called the "heater core". A fan circulates air through the core when hot air is needed. The control valve (solenoid valve) of the heater controls the amount of refrigerant flowing through the core of the heater in order to generate the necessary heat according to the needs set in the dashboard.


 
                                                                                                                                                                                       
                                                                                                                             
                                                                                                                                                                                                                                                                                                                                        

                                                                                                                                                                         FAE control valve
 
 

Functioning of a FAE thermostatic electrovalve. 
 

 
 
 
5. TEMPERATURE SENSORS: TEMPERATURE CONTROL OF THE LIQUID COOLANT


One of the most important elements in today's cars is the temperature sensor, which measures the temperature of the coolant liquid. The information, measured through a NTC (Negative Temperature Coefficient) which changes its resistance with temperature and which is located inside the sensor, is sent directly to the ECU (Engine Control Unit) or to the module management of the refrigeration system that will regulate the injection to adapt the combustion to the temperature of the engine. With a cold engine, the engine electronics improve combustion by enriching the mixture and regulating it constantly until reaching an ideal temperature. For example, at cold start, in the case of combustion failures and rapid temperature changes occurring in cold parts, the ECU modifies the ignition advance angle, the injection map, the oil injection capacity, the ventilation valve of oil, etc. so that all engine systems work under established parameters and mechanics do not suffer in the critical process.

The FAE temperature sensor is also used more and more to replace the temperature transmitters, to turn the fan on and off, as well as to indicate the temperature on the thermometer of the dashboard. Previously this function was performed by the so-called thermo-resistances, of which FAE manufactures a large number of references available in the market.
                                                                                                                                                                    Temperature sensor of the coolant liquid manufactured by FAE.
 
 
 
Dissection of a temperature sensor manufactured by FAE
 


FAE manufactures products for engine temperature management since 1952 and currently has a production of more than 2 million pieces per year with a coverage of over 97 countries, with more than 1200 references, both for European, Asian and North American applications.

If you want to know more about our products, visit www.fae.es/en/ or contact us at  fae@fae.es