The most basic observation we can make about a turbocharger is that it can be split into the hot and cold side. The hot side houses the turbine wheel and the cold side houses the compressor wheel.
All turbos are connected to the engine on their hot side. So as your engine is running it creates exhaust gasses. These exhaust gasses would otherwise be wasted, but on turbocharged engine these hot and fast moving gasses are used to drive the turbine wheel.
On the other side, the cold side, we have the compressor wheel. The compressor wheel has a fixed connection to the turbine wheel via a common shaft. So when you spin the turbine wheel, you also spin the compressor wheel. The compressor wheel shape is designed to suck in air into the turbo charger. It’s called the compressor wheel because other than sucking the air in, the compressor wheel plays an important part in compressing the air, after which it send the air through the compressor housing into your engine intake manifold and your combustion chamber.
This compression of air is what helps turbocharged engines make more power. So the turbo compresses the air, it stuff more air molecules into a given space and by doing so it increases the pressure of the air which leads to the natural question of how do we control the amount of pressure that a turbo generates.
Enter the waste gate. This is what controls the pressure created by the turbo. The waste-gate system consists of the actual waste gate and a waste gate actuator. So this part of the turbo housing and this plate of the cartridge play a key part in pressuring the air. When these two parts come together they create the diffuser. The diffuser turns the turbulent and fast moving low pressure air coming from the compressor wheel into slow moving high pressure air.
To understand how it does this we have to take a loot at the ideal gas law which states that gas pressure and volume are inversely proportional. This means that as volume decreases pressure increases and vice versa. And as you can see the shape of the diffuser incorporates a dramatic decrease in volume. The compressor wheel flings and stuff the air into the narrow space, this both slows it down and pressurizes it. The air then travels through the volute and into the engine.
As we said pressure and volume are inversely proportional, as one decreases the other increases. But pressure and temperature on the other hand are directly proportional. As pressure increases so too does temperature. And this makes sense, as you compress the molecules closer together they start making more contact, generating more friction and thus more heat. This is why turbos not only pressurize the air, they also heat it up. And this is why turbocharged setups very often include an inter-cooler. The intercooler cools the air back down to prevent the air fuel mixture in the combustion chamber from pre-igniting from being too hot.
Now let’s take a look at the turbo core. As you can see it consists of the turbine and compressor wheels and the center section which houses the shaft and some holes. This particular turbo is oil and water cooled. It has inlets and outlets for both engine oil and coolant. The compressor wheel on almost all automotive turbochargers is radial. This means that it sucks in the air straight in, but it compresses it in another direction, in most cases 90 degrees offset from the direction of the air entry.
Inside the turbo core we can also find some bearings. A turbocharger has two types of bearings. Ones that control the radial movement of the shaft and others that control the axial movement of the shaft. The bearings that control radial movement can either be journal bearings or ball bearings. Ball bearings can be beneficial in the sense that they can offer lower friction and faster turbo spool up time, however journal bearings are also adequate for a very wide range of applications.
The bearings that control the axial movement of the shaft are called thrust bearings. This video was basically turbo 101 and in our future videos we will keep diving deeper into the turbo with more detailed analysis of all of it’s components including different compressor wheel designs, waste gate types, bearings and much much more.
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