WORK Turbochargers

Turbochargers 101

In Turbochargers 101 we've provided detailed explanations of all the basics for you to review and better understand the basic functions of turbochargers and the associated elements of a complete turbo installation. WORK Turbochargers is here to help you!


What Is A Turbocharger?

In its simplest form a turbocharger is an exhaust driven centrifugal compressor that feeds your engine with more air than it can normally ingest allowing a greater amount of power to be produced than the same engine normally aspirated.  Since all internal combustion engines rely on oxygen to burn their fuel, feeding more air, or oxygen, by the use of a turbocharger, more power can be produced.  In most cases, power increases of 50-75% will be achieved with turbo charging.  Normally, the exhaust gas by product of the combustion process is expelled from the engine out into the atmosphere. A turbocharger utilizes this normally wasted gas as an energy source to drive the turbine wheel before being returned to the exhaust system.  The turbine wheel has a shaft that connects it directly to the compressor wheel located on the opposite end of the turbocharger.  This compressor wheel draws in fresh air from the air filter assembly, then compresses it to provide a force fed charge of air for your engine utilize in combustion.  The turbocharger spins at an extremely high speed, some models approach 160,000 revolutions per minute to provide enough air flow to feed a hungry engine.  The turbo relies on oil suspended bearings to allow its shaft to rotate.  The speed at which the turbo turns, combined with the heat generated by the exhaust system equates to a very sophisticated part made with very specialized materials, machined and manufactured to strict tolerances.  A turbocharger rebuilding process is very labor intensive and requires specialized equipment and strong experience, we recommend always sending your turbocharger to a professional for repairs any needed.

What Is A Wastegate?

On most turbocharger systems you will find a very important part commonly referred to as a waste gate.  Since the turbocharger relies on the engines exhaust to drive the turbine, at some point there will be an excess of airflow energy available, so the need to control that flow to the turbo and subsequently, the boost pressure being produced, is the job of the waste gate.  The function of this part of the turbo system is fairly straight forward; it provides an alternate passage around the turbine wheel for the exhaust gas to flow.  Usually connected to the waste gate valve is the waste gate actuator.  This actuator will have a boost reference tied into the engine intake manifold and is designed to “actuate” or move once a desired amount of pressure signal is received.  This movement opens up the waste gate valve, allowing the turbine speed to slow, therefore equalizing the boost pressure available in the intake manifold of the engine.  On most production gasoline cars this pressure will be between 8-14 PSI at the intake manifold.  Almost all production cars will have some type of computer control over this pressure; usually this will be in the form of a waste gate control solenoid located in line with the vacuum signal going from the intake manifold to the waste gate actuator.  Allowing the computer to control the given boost is a safe guard against damage due to poor quality gasoline, differences in atmospheric conditions or even the load being placed on the engine due to gear position or operating conditions.

What Is A Compressor Bypass Valve?

Since a turbocharger’s drive energy is provided by the exhaust gases and its operational speed is dictated by engine load, a turbocharger has a very dynamic operating speed range.  When you are sitting still in traffic with your car at idle speed, the turbocharger is spinning at about 1/8th of it total capability.  Once you start to accelerate by opening the throttle its speed increases dramatically. In most cases it approaches 100,000 rpm or greater.  As you reach your comfortable speed and let off the throttle, the throttle plate partially closes to reduce the amount of air feeding the engine, but the turbochargers rotational speed carries a lot of inertia and once the throttle is closed the result is a pressure spike generated when the compressed air has nowhere to go.  The job of the compressor bypass valve is to relieve that pressure spike by bleeding off the unwanted air and redirecting back into the air filter assembly.  This keeps the turbocharger from enduring high amounts of load due to the rapidly changing rpm that is encountered while driving.

What Is An Intercooler?

The turbocharger is centrifugal compressor, and one of the by products of compressing air is the heat generated by that actual act of compression.  The design of the blades of today’s turbochargers compressor wheels make them very efficient, providing for the means of filling the engine with a large amount of air very quickly.  The high operational speeds of the compressor introduces a significant amount of heat into the air that needs to be reduced before it enters the engine, this is the job of the intercooler.  The intercooler in most cars uses ambient air passing over a radiator type core to cool the charged air.  Since the compressed air directly out of the turbocharger can approach 300*F, and most outside air temperatures are 100*F or less, the ambient air does a really good job cooling the intercooler and charged air before it reaches the engine.

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Turbocharger Part Definitions:

We've broken it down even further for you! Here is a list of common parts with explanations of their function along with photos. A quick study of the details here will not only make you sound like a pro at the track, you'll gain a solid idea of common parts and terms used in the world of turbochargers.


Compressor Housing

This is usually an aluminum housing that contains the volute that will channel the air from the air filter assembly to the compressor wheel and finally out to the intercooler plumbing.  It's design and function are fundamental to the centrifugal compressor family, usually the housing will have a volute or scroll design that is used to promote air flow and pressure for the engine.

Shaft Nut

Retains the compressor wheel and thrust collar to the turbine shaft

Compressor Wheel

The compressor wheel is located in the compressor housing. It is usually made of aluminum, either cast or forged milled billet.  The compressor wheel pulls air from the air filter assembly and then centrifuges it at a high rate of speed into the compressor housing volute to produce pressure to feed the engine.  Compressor wheels are often measured in the exducer or major dimension, with the inducer being called the compressor wheel trim.
 

Back Plate, or Seal Plate

This connects the bearing housing to the compressor housing and serves many purposes.  Besides being a method of attachment, this plate usually provides the sealing surface for the compressor side seal.  It is also the diffuser for the compressor wheel exducer to compressor housing volute, and also the retaining device for the thrust bearing system.

Compressor Piston Ring

The compressor side piston ring is a circular spring steel ring that is used to provide a dynamic  seal between the back plate and thrust collar.  This seal relies on the design of the thrust collar and proper clearances to provide both oil control as well as keeping contaminates from entering the bearing system from the compressor side of the turbocharger.

Star Spring

Used to retain the thrust bearing in some turbocharger designs

Quad Ring

a simple sealing ring located between the back plate and bearing housing

Thrust Bearing

The thrust bearing in a turbocharger is the main locating structure for axial movement.  Axial, or “in and out” movement must be held in tight tolerance to maintain the exact clearance needed between the compressor and turbine wheel to housing relationship.  Thrust bearings can be made of bronze alloy, sintered iron or steel alloys depending on application.  All thrust bearing designs utilize hydro-dynamic action with oil as the medium to eliminate friction and allow precision location at high speeds.

Thrust Collar

The job of the thrust collar is to provide a locating surface between the sides of the thrust bearing.  The thrust collar also provides the compressor side seal ring or carbon seal a location point.  The collar fits around the thrust bearing usually within .0025” of nominal clearance.

Bearing Clip

Locates the journal bearings in their proper location within the bearing housing

Journal Bearing

Bronze bushing used to locate the turbine shaft radially within the bearing housing.  These are usually full floating hydro dynamic bearings that rely on oil film to provide operation at high speeds.

Bearing Housing

Usually cast iron, the bearing housing locates the bearings, provides the oiling circuits for the thrust and journal bearings and in some cases has water cooling passages to aid in the cooling of the turbocharger.

Heat Shield

Protects the back of the bearing housing as well as the turbine side piton ring seal from direct heat generated by the flow of exhaust through the exhaust housing.

Turbine Piston Ring

The turbine piston ring is a circular spring steel alloy that is used to provide a dynamic seal between the turbine wheel and bearing housing.  This seal relies on the turbine wheel design to keep oil away from the turbine housing as well as exhaust gases from entering the bearing housing assembly.

Turbine Wheel

The turbine wheel and shaft assembly transfers the exhaust energy radially to the compressor wheel.  Turbine wheels are usually made of Inconel or other high temperature alloys to allow them to perform in a temperature environment that regularly exceeds 1500*F.  The turbine wheel also holds the turbine side piston ring, provides the bearing surface for the journal bearings to ride and also has the quill that holds the thrust collar, compressor wheel and shaft nut.  Turbine wheels are usually measured by inducer dimension in millimeters and exducer dimension in trim.

Turbine Housing

The job of the turbine housing is to collect the exhaust gases and direct them through a volute to the turbine wheel inducer.  This increases the velocity of the exhaust gas and provides the drive energy for the turbine wheels rotation.  The turbine housing will usually be made of cast iron, or other high temperature alloys.  Some turbine housings will have the wastegate valve built in to the housing.

Wastegate Actuator

The wastegate actuator uses a diaphragm and spring to hold tension on the wastegate valve assembly.  The spring is calibrated to a specific pressure, and once that pressure is achieved at the intake manifold it is channeled into the actuator body through a port connection.  This pressure moves the actuator rod, opening the wastegate valve and regulating boost pressure.

Rotating Assembly

Most standard turbocharger designs have a rotating assembly that consists of the turbine wheel, thurst collar assembly, compressor wheel, and shaft nut. It is important if any one part of this assembly is changed, that the unit as a whole be rechecked for proper balance.

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