Roots type Supercharger

Roots-Type Supercharger - Operating Principles

Jump to:
1. Overview
2. How It Works – Step by Step
3. Key Components Involved
4. Common Misconceptions
5. Why This Matters

Anchor 1

Plain-English summary: what the system does

A Roots-type supercharger is a positive-displacement air pump used to increase the mass of air entering an engine. It delivers pressurised intake air by mechanically moving fixed volumes of air from the inlet to the outlet. By increasing the amount of oxygen available for combustion, a Roots blower enables the engine to burn more fuel and produce greater torque and power, particularly at low engine speeds.

How it Works - Step by Step

Anchor 2

Mechanical drive
The supercharger is driven directly by the engine, typically via a belt connected to the crankshaft. This ensures airflow increases in proportion to engine speed.
Air entry
Ambient air passes through the intake system and enters the supercharger housing at the inlet ports.
Air trapping
Inside the housing, two intermeshing rotors rotate in opposite directions. The rotors do not touch each other or the housing. As they rotate, pockets of air are trapped between the rotor lobes and the casing.
Air transfer
The trapped air is carried around the outside of the rotors from the inlet side to the outlet side. The air is not compressed internally within the blower.
Pressure rise at the outlet
Compression occurs when the transferred air is forced into the engine intake manifold, where it meets existing pressurised air. This causes a rise in pressure.
Charge cooling (where fitted)
Because the air temperature increases during pressurisation, an intercooler is often used downstream of the supercharger to reduce air temperature and increase air density.
Delivery to the engine
The pressurised, cooled air enters the combustion chambers, allowing more fuel to be injected and increasing engine output.

Key Components Involved

Anchor 3

Rotor pair
Two lobed rotors that trap and convey air from inlet to outlet. Modern designs often use twisted lobes to reduce noise and vibration.
Supercharger housing
A precision-machined casing that contains the rotors and defines the airflow path.
Timing gears
Synchronise rotor motion to prevent contact between the rotors.
Drive system
Typically a belt and pulley arrangement transferring rotation from the engine crankshaft.
Inlet and outlet ports
Openings that allow air to enter and exit the supercharger.
Intercooler (where used)
A heat exchanger that reduces intake air temperature after pressurisation.

Common Misconceptions

Anchor 4

“The Roots blower compresses air internally”
A Roots supercharger moves air but does not significantly compress it within the housing. Pressure increases mainly in the intake manifold.
“The rotors touch to seal the air”
The rotors are precisely timed and do not make contact. Contact would cause rapid wear and failure.
“Superchargers only increase peak power”
Roots superchargers are particularly effective at increasing low-speed torque due to their direct mechanical drive.
“Cooling is optional”
While the engine can operate without charge cooling, cooler intake air improves efficiency and reduces thermal stress.

Why This Matters

Anchor 5

Roots-type superchargers provide immediate airflow increase with no reliance on exhaust energy. This makes them well suited to applications requiring strong low-speed torque and predictable response. Understanding their operating principle explains their characteristic performance, efficiency limits, and the importance of intake air temperature control.

Quick Reference

Induction type: Positive displacement
Drive method: Mechanical (engine-driven)
Compression location: Intake manifold
Key characteristic: Immediate boost and strong low-speed response