Automotive Supercharger Types: Roots, Lysholm, and G-Lader

Roots Compressors

The Roots compressor, often referred to as a lobe-type compressor, is a widely recognized design. It utilizes a pair of rotors shaped like the number "eight," connected to gears that spin at the same speed in opposite directions to pump air. This device primarily moves air rather than compressing it internally. Because the rotors never touch, they experience minimal wear. However, Roots compressor efficiency is relatively low and decreases as engine speed increases, with volumetric capacity exceeding 50% only within a very limited range. Additionally, the compressed air becomes extremely hot. These rotors may feature two or three lobes.

Comprex Pressure Wave Superchargers

The Comprex system leverages the principles of a volumetric compressor and a turbocharger to create a highly efficient machine, though it possesses distinct drawbacks. It facilitates energy transfer between exhaust gases and supply air through pressure waves generated between the thin radial walls of a drum, which rotates via a direct connection to the crankshaft. This combines the benefits of a turbocharger by utilizing exhaust gas power, while the rotor drive requires only a small amount of engine power to maintain the pressure wave process. While this compressor performs exceptionally well on diesel engines, it suffers from mechanical complexity, noisy operation, and high manufacturing costs.

Lysholm Compressors

The Lysholm compressor consists of two meshed, rotating helical components. As air enters between these parts, the spinning motion decreases the volume, thereby increasing air pressure. Typically driven by the crankshaft via a belt, the Lysholm compressor achieves approximately 80% efficiency. It can reach speeds of up to 12,000 rpm to ensure sufficient boost for increased torque. Operation is controlled by an electromagnetic clutch—similar to those used in air conditioning systems—managed by the Engine Control Unit (ECU). The ECU also regulates a bypass valve; when the valve is open, the compressor is disengaged, allowing the engine to operate as a naturally aspirated unit. When boost is required, the clutch engages and the valve closes, providing the necessary pressure for rapid acceleration.

G-Lader Compressors

The G-Lader, a type of centrifugal charger famously used by Volkswagen, is named for the "G" shape of its internal chambers. The internal components move in an eccentric, non-rotating motion. It features a movable element arranged eccentrically with a spiral structure on both sides, which, combined with fixed spiral covers, creates chambers of variable volume. These units were largely discontinued in the 1990s due to persistent lubrication and sealing issues.