Internal combustion engine cooling
The cooling system in an internal combustion engine mainly performs from the heat that is delivered to the walls of the combustion chamber and the cylinder, because the process is not ideal circle. Too high temperatures would damage the engine ( tearing of the lubricating film, burning the valves). In Stirling engines, the process heat to be dissipated via the cooling is delivered.
The primary cooling system air cooling and water cooling are used. There are also - mostly for air cooling - cooler for the lubricant to keep the engine at operating temperature.
- 2.1 Advantages and disadvantages
- 2.2 coolant circuit
- 2.3 components 2.3.1 cooler
- 2.3.2 Cooling Fan
- 2.3.3 coolant pump
- 2.3.4 thermostat
- 2.3.5 Expansion vessel
Air cooling
Characteristic are the metal fins around the cylinder and the cylinder head. The air in relation to the much larger heat conductivity dissipates the heat, the large surfaces favor the transfer to the surrounding air.
Use
Currently, the air cooling is used mainly in aircraft engines, motorcycles, small engines from lawn mowers or chain saws. Historic motor vehicles, this engine design are in passenger cars and Others, the Citroën 2CV ( " duck " ), Honda 1300, Porsche models 356 and 911 (until 1998), VW Bus (up to 1982), VW Beetle, all Trabant except Type 1.1, as well as cars and trucks and Tatra trucks from Magirus -Deutz and Robur.
Pros and Cons
Simple and inexpensive construction Up faster ( in the presence of appropriate regulatory devices ) No freezing of the coolant at low outside temperatures Reliable operation, maintenance-free For aircraft and military aircraft: low shelling sensitivity Distinctive noise (which may be a desired effect under certain circumstances, especially in sports cars )
- Excessive noise - Distribution of cooling air is not perfectly possible engine power limited by - Cooling fan, if present, operates with high output cost ( up to 8 % of the engine power) - Detecting the engine temperature hardly possible - With faults: danger of uncontrolled overheating of the engine - Heating of the passenger compartment hardly possible
Components
Cooling fan
Many small engines, but also motorcycle engines usually come from without fan. In other applications, a cooling fan is used for acceleration of the active heat exchange. The fan is mostly driven by the alternator belt, so a tearing of the same here is particularly problematic, the vehicle must be stopped immediately. A cooling fan is also often used in stationary engines, for example, in power or compressed air units, for vehicles with low speed ( mopeds ) or other thermally highly stressed engines.
Cooling air flow
The air is - mostly out of baffles - blown directly on the engine. The cylinders and cylinder heads air-cooled engines have fins to increase the heat dissipating surface.
Cooling air regulation
In order to achieve the optimum working temperature quickly even at low outdoor temperature, some have air-cooled engines thermostat-controlled valves, for example, the corresponding VW engines.
Oil cooler
With many types in addition, the engine oil is cooled. Older Deutz engines it is pumped through a spiral-shaped conduit system is in " wind tunnel " of a cooling turbine.
Liquid cooling
Modern four-stroke engines are liquid-cooled, with few exceptions, where a mixture of water and antifreeze and corrosion protection products serves as a coolant in the rule. Therefore, in general parlance, the term water cooling has prevailed.
Pros and Cons
Water has a uniform heat transfer and can dissipate a large amount of heat. The refrigerant circuit is operated with a slight excess pressure so that coolant temperatures up to about 115 ° C are possible and prevents cavitation of the cylinder walls. The system is thereby protected by a pressure relief valve. The liquid cooling keeps the temperature difference of individual engine components, and thus the potential delay, low. This, in turn, to increase power density of combustion engines allowed. For cooling, less power than the cooling fans of air cooling is required Heating in closed vehicles is very easy to operate by a heating heat exchanger ( heat exchanger). The water jacket to avoid contact noises
- The engine block, and thus the necessary molds are expensive to produce. - Elaborate and thus error-prone design: cooler and water pump are subject to wear, coolant must be maintained regularly ( especially in tropical areas can be a problem ) - Engine reaches its operating temperature only slowly, especially in the Thermosiphonkühlung
Coolant circuit
A water cooler or coolant cooler, which often is used to generally made of brass, aluminum is now usually attached to the front of the vehicle, where an air stream is cooled by the flowing coolant. From there, the coolant is a water pump through hoses to the engine pumped (cylinder head and engine block ). To allow even at low engine speed a good cooling, electric water pump (power ~ 200 W) are used in modern engines. The coolant circulation is produced by the water pump. Another active principle having a simple structure has the Thermosiphonkühlung used in the past.
Components
Cooler
Modern liquid cooled in the car consists of a condenser with a large surface area, which is typically mounted between the front headlights. Condensers of air conditioning or charge air coolers are installed in front of the radiator.
Radiator fan
Before or behind the radiator there is a fan. Classically, the fan via a belt drive with the engine crankshaft is connected and therefore all the more requires more power, the higher the engine speed. To reduce the power have some cooler fans via an intermediate viscous coupling that regulates the speed of the fan depending on the temperature. Since the 1980s, cooling fans are driven mainly with electric motors, which are controlled by a thermal switch mounted in the cooler. These fans are tuning in only when needed.
Coolant pump
The water pump is normally otherwise driven by the toothed belt or a V- ribbed belt. Formerly the fan was also driven and ran constantly with. On the front side of the radiator shutters were also sometimes attached to it. During the cold season with a cable operated from the driver's seat allowed, heraufzuregeln by closing the motor temperature slightly Where this was not possible, and sometimes boards were temporarily placed in front of it. Nowadays, these blinds are back in the luxury segment to be found, however, electronically controlled (eg BMW X5). But they are used to improve the aerodynamics and thus reducing fuel consumption, lower in relation to the cooling.
But there are also viscous fan with a temperature-controlled coupling ( viscous coupling ), in which the torque is transmitted through a highly viscous working fluid without touching the clutch parts and wear-free. This saves fuel, and the engine power is at a lower noise emission higher than during continuous fan drive.
Thermostat
The cooling circuit, and thus the engine temperature is controlled by a thermostat. As long as the engine has not reached operating temperature, the thermostat valve is closed and the coolant circulates only from engine, water pump and heater core. The thermostat opens, the main water cooler is included with the circulation, and the actual cooling begins. The thermostat valve opens at approximately 75 degrees Celsius. In the luxury segment, there are now also motors with multiple loops and map-controlled electric thermostat.
Exceeds the temperature of the coolant a further threshold value, which is typically 90 degrees Celsius, the electric fan is turned on by a thermostatic switch. When the system is intact, this only happens at slow speeds. Depending on the electrical wiring of the cooling fan can continue for some time even with the ignition off.
Expansion vessel
Since the cooling fluid expands when heated, the pressure in the cooling system. To compensate for this effect, a reservoir / expansion tank is integrated in the cooling circuit, which receives the excess refrigerant and gives off again as required. By increasing the system pressure at the same time increases the boiling point of the coolant.
Coolant
The liquid cooling system also has several disadvantages: In extreme cold can freeze the coolant and cause the engine block to burst. In order to avoid freezing of the system at low outdoor temperatures, special additives must be added to the cooling water. These so-called antifreeze also prevent the formation of rust inside the motor. Usually a water -glycol mixture is used as the cooling medium.
Overall reliability
Through additional failure modes such as leaky cooling circuit, defects in water pump, radiator, belts, or thermostat, the reliability decreases.
Cab heating
In addition, the warm cooling water is also used for the car heater. It can be used to a limited extent, for cooling the engine when the thermostat and / or the fan are defective: The operation of the interior heating at a high fan speed and temperature adjustment of the maximum air flow is passed through the heat exchanger and thus removed substantial amounts of heat to the cooling circuit of the engine.
Oil cooling
The term is equally used for:
- When electrical equipment is often a water cooling is not possible because water more or less is conductive ( See also: Oil Cooling ).
- As a special form of liquid cooling ( colloquially water cooling) is on an internal combustion engine as the cooling medium used oil instead of water, such as when Deutz FL1011. Here, the existing lubricating oil is also used for cooling the cylinder liners, or in addition to the cylinder heads.
- In highly loaded engines piston cooling is common by lubricating oil ( skirt piston oil cooling), but also the cooling of auxiliary units (eg emplacement of the turbine shaft with turbochargers ).
- If sufficient heat can not be dissipated through the crankcase surface cooling is required ( see below for details ) for the lubricating oil.
In order to obtain the lubricating properties of the engine oil, a controlled heat dissipation is required. As usual limit apply 120 ° C; about the rule of thumb that for every 10 degree rise in temperature halves the life of the oil. For this reason, many engines oil -air heat exchangers have (oil cooler) or an oil -water heat exchanger, depending on which medium the heat to be transferred.
Further cooling systems
The engine cooling system is not always the only cooling system in an engine or vehicle. In addition, even separate systems for the charge air, engine oil, transmission oil, power steering fluid, or the fuel can be installed. In hybrid vehicles, usually there is another cooling system for cooling of electric motors / generators and their power electronics (eg inverters, inverter).