In a simplified way, the supercharging is any process that allows to increase the amount of air admitted by the engine. The two main ways to achieve this increase are by decreasing the temperature of the admitted air and by increasing the supply pressure.
In the car these two processes are often combined, in supercharged systems, increasing the intake pressure, and with intercooler, decreasing the air temperature, increasing the density and volumetric efficiency of the engine.
The main elements of a turbocharger are the component body, called core and shown in Figure 1, the intake and exhaust snail.
This element has high importance for the component, it is where the various lubrication elements and the rotor, set consisting of the compressor, turbine and respective shaft are housed.
The rotor is shown schematically in Figure 2.
The identification of each rotor element is performed next.
1. Turbocharger compressor
3. Lubrication bushings
4. Shaft from the turbine
Operation - Supercharged system
The operation of a conventional supercharged system is shown in Figure 3.
Inside the MCI (Internal combustion engine), combustion of the mixture (air and fuel) occurs giving rise to the exhaust gases. The formed gases are then expelled to the exhaust, radially enter the exhaust turbocharger snail, activating the turbine, transmitting movement and then being expelled axially.
The turbine and turbocharger shaft are solidary, and are then coupled to the compressor. Therefore, the movement transferred from the exhaust gases to the turbine is also transmitted to the compressor, leaving the entire rotor (see Figure 2) in rotation.
The air before being admitted by the engine enters axially into the inlet snail, where it is compressed by the compressor. Air compression causes an increase in gas pressure and temperature, being cooled in the intercooler and later admitted by the engine.
Given the operation of a turbocharger, where energy is transferred from the exhaust gases to the rotor in order to increase the pressure of the admitted air. The component is more efficient at high engine speeds, starting at 2000 rpm. At lower engine speeds, the exhaust gases still do not have enough energy to increase the rotor speed, which can reach 300,000 rpm at high speeds.
Today's vehicles are increasingly complex and there is more and more interaction between the various vehicle systems. Therefore, the malfunction of a system can affect the performance of the others.
As explained earlier, a turbocharger allows you to put more air into the engine and thus inject more fuel, causing a significant increase in power in the MCI. However, the increase in power is not the only reason for manufacturers to use turbochargers. The component directly influences consumption, allowing low emissions, reduces the level of emissions, influences the functioning of the EGR valve, affects the operation of the particulate filter and even the operation of the automatic gearbox.
Maintenance and prevention
In order to guarantee the correct functioning of the component and extend its useful life, the maintenance performed on the vehicle is extremely important. Regarding this aspect, LD Auto recommends that the service is performed by specialized technicians and that all manufacturers' plans and standards are followed.
To extend the life of the turbocharger, it is important to:
The main faults in turbochargers are often caused by a lack of maintenance.
Turbocharger assembly - New, rebuilt or repaired
After damage, also in the assembly of a new or repaired component, some care and checks are necessary in order to successfully complete a repair.
No joints or connection points should be replaced by glue or silicone, as these products may contaminate or obstruct the system.
Most frequent breakdowns
The most frequent breakdowns in turbochargers are caused, as a general rule, by lack of maintenance of the vehicle or by breakdowns external to the component in adjacent systems.
Some of the most common problems are:
Excessive axial clearance - Wear of the turbocharger components that cause a rotor displacement on the horizontal axis.
Figure 4 shows a set of photographs of a turbocharger with excess axial clearance.
The turbocharger shown in Figure 4, had the core (see Figure 1) damaged and with excessive axial clearance. The main cause of axial clearance is obstruction in the exhaust line. Due to the obstruction in the exhaust, the rotor (see Figure 2) works subject to forces that press the assembly and all internal components to the intake side, impairing lubrication and causing premature wear on all components.
It is possible to see great wear and tear on various components of the turbocharger. The axial and washer of the same show high wear, visible in a), the force caused by the obstruction and increased clearance, caused the turbine base to be damaged against the fire plate (marked with a green arrow), visible in b) and c), releasing material that later damaged the fins of the turbocharger geometry, visible in d). As the problem worsened and the axial clearance increased, the blades of the compressor and the respective inlet cap came into contact and both components were also damaged, the compressor is shown in e) and the interior of the cap in f) where it is great wear is visible in the internal area where the two components worked in contact.
The main cause of exhaust line obstruction in today's diesel vehicles is the back pressure generated by the obstruction of the particulate filter and catalyst
Excessive radial clearance - Wear of the turbocharger components that cause the rotor to move perpendicularly to its axis.
Radial clearance is mainly caused by poor lubrication, that is, lack of oil, clogged oil channels or contaminated oil.
Figure 5 shows a set of photographs of a turbocharger with excess radial clearance.
In Figure 5 in a) an axial with wear marks is presented, however very different from those visible in Figure 4. In this case the axial is scratched and in some places it has deeper marks that suggest that there was a passing of chips in the place. However, although the component is badly damaged due to poor lubrication, it has more influence on the axial clearance.
The components of photographs b), c) and d) of Figure 5 mainly contribute to the radial clearance. In b) one of the bushes where the shaft works is shown, as it is visible, it presents high wear, it has a grip and next to the lubrication hole subtraction of material. In c) the turbine shaft and the various zones of the turbine with signs of seizing are visible in the areas where the bushings are located. Finally, in d) is a photograph that highlights the appearance of a zone of the turbine shaft, due to the turbocharger running out of oil or with contaminated oil.
Entry of foreign objects
Damaged turbochargers are often found due to objects entering the interior. Depending on the type of object, damage to the turbocharger can vary.
Figure 6 shows the most common situations of foreign bodies entering the component. In Figure 6 in a), it is verified that there is an excessive gap between the compressor and the inlet snail. This gap originates from the passage of small material such as dust or sand and is an indicator of a very dirty or damaged air filter. In Figure 6 in b), a compressor that is severely damaged due to the passage of a foreign body to the intake snail is visible. Finally, in c) there is a turbine damaged due to the passage of a foreign body to the exhaust, such as candle tips or material released by the exhaust manifold.
Forced oil passage
There can be several causes for forced oil flow in a turbocharger, clogged oil return channels, faulty engine operation with low compression or defective injection.
Figure 7 shows a set of photographs of a turbocharger with forced oil flow.
The component in Figure 7 had acceptable and normal clearance levels, however the intake had a lot of oil, as shown in Figure 7 in photographs b), c) and d). In addition, the turbocharger shows signs of overheating in the exhaust, visible in photographs e) and f), confirmed by the discoloration of the turbine and the bluish hue of the exhaust snail.
In short, the turbocharger is an extremely important component for the proper functioning of the vehicle. Although it does not require maintenance to be performed directly, it is dependent on the maintenance and operating status of the various systems that are adjacent to it, upstream and downstream of the system.