Heat, from the birth of the car, has always been indispensable to the car. The engine drives the car, which requires fuel combustion to do the work, and the heat released by the combustion is particularly important for the work of the car.
Too little heat will make the car unable to fully enter the working state, and too much heat will make the car malfunction. Therefore, for the management of heat, it has always been a problem that car companies need to solve, even if it is into the era of electric vehicles, the thermal management of the three-electric system is the same.
So how do car companies solve the thermal management problem of automotive powertrains?
In the engine, fuel combustion does the work to power the car. But the heat that comes with it is not what the engine needs. Engine overheating can cause serious damage such as burst cylinders.
However, due to the technical limitations of the time, the engine did not have a very complex cooling system, and air became the only medium for engine cooling. Through the cylinder block directly in contact with the outside air, to achieve the effect of cooling the engine.
This cooling method is very simple and at a low cost, requiring only a special design of the outer surface of the cylinder block to achieve the cooling effect. Including many motorcycle engines, especially small displacement engines, are air-cooled engines, and the engine heat sink seen on the cylinder block is actually the most important source of engine cooling.
The advantage of air cooling is naturally that the structure is simple and lightweight, and the cost is extremely low, but the lower cooling efficiency makes it now only for ultra-small displacement engines. Many low-cost motorcycle engines now use air-cooled. Like the most common kind of 125cc motorcycle, because of the small displacement and small power, the cooling requirements are relatively low.
But when it comes to larger displacement engines, air cooling cannot meet the requirements of higher power output. At this time, water cooling has become the only way to cool.
Large-displacement engines have multiple cylinders, and the heat generated together will be higher, and the power output of the engine is limited by the ability of wind and cold. This is also one of the reasons why the power output of the large-displacement multi-cylinder engine of a few decades ago was not as good as the current 2.0T.
But why water? The reason is that its heat absorption capacity is the strongest of all substances.
The specific heat capacity of water is 4200J/(kg·°C), and it is said that 1kg of water can absorb 4200J heat by raising °C. Therefore, the heat absorption efficiency of water is very high. If you use water to absorb the heat generated by the engine, and then release the heat into the air through other heat exchange methods, the heat dissipation effect will be much better than direct air cooling.
Whether it is a fuel vehicle or an electric vehicle, the heat dissipation method of modern automobiles is based on this way.
In the cylinders of an internal combustion engine, the combustion temperature of the fuel can be as high as 2500 ° C, so the cooling of the cylinders and cylinder heads is the highlight of engine cooling.
Cooling water in the engine through the water pump into the engine block, the engine cylinder body of the cooling water channel mainly around the cylinder, before I also mentioned that the cylinder combustion temperature is very high, so the use of cooling water first cooling cylinder effect is the best. After cooling the cylinder block, the cooling water will enter the cooling channel of the cylinder head, which is also the most important component of the engine to receive heat. After cooling the cylinder head, the cooling water will return to the cooling tank and exchange heat with the air to dissipate the heat absorbed after the round just passed.
The water cooling system mentioned above can only be regarded as relatively basic, and does not fully play the advantages of the water cooling system, because the different components of the engine have different requirements for cooling under different working conditions.
Back to the water cooling route I just mentioned, the cooling water has absorbed a large part of the heat after passing through the cylinder block, and if you go to cool the cylinder head at this time, the cooling water will be insufficient due to insufficient heat absorption capacity.
In addition, the most basic cooling system, its pump power is obtained from the front pulley train of the crankshaft, which means that its pumping speed is proportional to the engine speed. However, in some low-speed and high-load conditions, insufficient pumping capacity of the pump will also lead to a decrease in cooling efficiency.
So in the engine cooling system, there will be some more special designs.
The 1.5-liter Snap Cloud engine used by BYD DM-i uses an electronic water pump and split cooling technology. The electronic water pump is a pump driven by an electric motor, and its speed is not related to the speed of the engine, so in the working conditions of low speed and high load, the electronic water pump can still provide sufficient cooling water to the engine.
With two electronic thermostats, the Snap Cloud 1.5L engine also solves another problem - the lack of cooling water supply when the engine starts, resulting in slow warm-up, which is very important for hybrid special engines that often start and stop.
In addition, for the cooling of the engine block and the cylinder head, BYD is also equipped with split cooling technology for the engine, in short, the cylinder cooling and the cylinder head cooling are divided into two cooling circuits, no longer cooling water first cooling the cylinder block and then cooling the cylinder head, through two thermostats to control two cooling circuits, improve cooling efficiency.
Electrified components such as electronic water pumps and electronic thermostats are highly efficient for cooling systems. This, of course, also depends on the higher voltage of the vehicle's electrical system. Whether it is the 48V, which is now the favorite european car, or a higher voltage hybrid car, the support of the electrical system is very important.
In fuel vehicles the engine requires a powerful cooling system for cooling. In electric vehicles, the cooling of batteries, motors and electronic control systems is also indispensable. And the most suitable temperature for the battery is around 50 ° C, the operating temperature range is narrower than that of the engine, and the thermal management system must not only know how to cool, but also know how to heat in an extremely cold state.
Therefore, many pure electric vehicles or PHEV models use cylindrical batteries. Although the cylindrical battery lags slightly behind the space utilization rate compared with the soft pack battery, the gap formed by the stacking of the cylindrical battery allows the cooling water to flow and the cooling efficiency will be higher. For example, the 6.1kWh ternary lithium battery used by the Mercedes-AMG GT63 e Performance has a cooling channel in the middle of the cylindrical battery cell, and the BMW i3 has a similar design.
However, for battery heating, many car companies have different solutions.
For example, The Krypton 001 uses a high-pressure liquid heater developed by Geely and BorgWarner. By heating the cooling circulating fluid, the battery is guaranteed to reach the operating temperature at low temperatures, while providing better heating for the crew compartment.
High-temperature liquid heaters use thick film element (TFE) technology to meet the needs of high-performance systems that generate heat quickly, while achieving minimal power loss due to the small thermal resistance between the heating element and the coolant in the high-pressure heater.
In fact, the thermal management of the car is a rather complex subject, and it is still the same in the era of electric vehicles. Now whether it is the performance of the battery itself or the heating in the car, even if the heat pump air conditioner is used, the effect is not ideal. The thermal management of electric vehicles in the future also requires a multi-pronged approach and a variety of measures to solve problems.