How a Turbo Works

WHAT IS A TURBOCHARGER?

• Forces more air into the engine at higher than ambient pressure.
  

WHY DO WE NEED MORE AIR ?

How does the Turbo work?

TURBINE

• A turbine wheel is driven by the otherwise 'waste' exhaust gases. The turbine is connected to a compressor wheel and the whole assembly rotates at speeds up to 230,000 rpm.
  

COMPRESSOR

• Ambient air is drawn into the turbo via an air filter, then, as it passes over the compressor wheel it accelerates up to very high speed.

• Once past the compressor wheel it passes through a 'diffuser' which is formed between the face of the backplate (or centre housing) and the machined face of the compressor housing.
  
  
• As it passes through this area the air moving at high speed slows down and this continues as it passes though the 'volute' of the compressor housing (shaped like a snail's shell!). This turns the Kinetic energy of the moving air into high pressure air.

Turbocharger Gas & Air Flow

Turbocharger Gas & Air Flow - On Engine

Turbocharger Construction

1 Shaftwheel Assembly

• The machined shaft and investment cast turbine wheel are joined by Inertia Welding or Electron Beam Welding

• Samples of the weld tested for hardness in heat affected area
• Weld penetration checked

2 Centre Housing

• Sand castings in various material grades
• Tested for porosity and for dimensional accuracy
• Bearing bore finish is critical surface
• Some use oil squirt hole for additional cooling

3 Thrust assembly - the thrust bearing
Sintered bronze or sintered iron

• Many different designs
• 270 degree or 360 degree

3 Thrust assembly - the thrust collar

Multi function

• Controls axial movement
• Separates oil and gases (oil thrower or slinger)
• Piston ring dynamic seal

Compressor End Dynamic Seal

4 Journal bearings

• Most fully floating
• Some semi floating

• Both designs use two oil films.......................

5 The compressor wheel

• Many different designs
• Rely on high speeds for efficiency
• Flatback and EBD

6 The CHRA