Twin-screw type supercharger
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The twin-screw type supercharger or twin-screw blower is a positive displacement type device that operates by pulling air through a pair of meshing high-tolerance screws similar to a set of worm gears. Twin-screw superchargers are also known as Lysholm superchargers (or compressors) after its inventor Alf Lysholm.
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[edit] Technical considerations
The intake is located at one end of the two screws, which overlap, but not completely, leaving a small pocket open. As the screws turn the pocket moves towards the exhaust side, pulling air in from the intake. As the air moves axially through the housing, space becomes smaller and the screw continues to pressurize the air charge. This air gets released via the built in pressure ratio discharge, which holds the compressed air to a specified pressure before exiting the compressor, thus leaving the compressor at a higher pressure than the chamber the air is entering. This causes low leakage levels and low parasitic losses vs. roots-type. The supercharger is typically driven directly from the engine's crankshaft via a belt or gear drive. Unlike the Roots type supercharger, the twin-screw exhibits internal compression which is the ability of the device to compress air "within" the housing as it is moved through the device.
High-precision CNC manufacturing techniques make the screw type supercharger a more expensive alternative to other forms of available forced induction. With later technology, manufacturing cost have been lowered while performance increased.
All supercharger types benefit from the use of an intercooler to reduce heat produced during pumping and compression.
[edit] Comparative advantages
A clear example of the technology applied by the twin-screw in companies like Ford, Koenigsegg, Mercury Marine and Mercedes can also demonstrate the effectiveness of the twin screw. While some centrifugal superchargers are consistent and reliable, they typically don't produce full boost until near peak engine rpm, while positive displacement superchargers such as Roots type superchargers and twin-screw types offer more immediate boost.
Many cold-air kits, exhaust upgrades, and most often any engine upgrade can often be retained when installing an after market twin screw.
[edit] Related terms
The term "blower" is commonly used to define a device placed on engines with a functional need for additional airflow. The term blower is used to describe different types of super chargers. A screw type super charger, roots type super charger, and a centrifugal super charger are all types of blowers.
