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Aconstant speed drive (CSD) also known as a constant speed generator, is a type oftransmission that takes an input shaft rotating at a wide range of speeds, delivering this power to an output shaft that rotates at a constant speed, despite the varying input. They are used to drive mechanisms, typicallyelectrical generators, that require a constant input speed.
The term is most commonly applied tohydraulic transmissions found in theaccessory drives ofgas turbine engines, such as aircraftjet engines. On modern aircraft, the CSD is often combined with a generator into a single unit known as anintegrated drive generator (IDG).
CSDs are mainly used onairliner andmilitary aircraft jet engines to drive thealternating current (AC) electrical generator. In order to produce the proper voltage at a constant AC frequency, usually three-phase 115 VAC at 400 Hz, an alternator needs to spin at a constant specific speed (typically 6,000 RPM for air-cooled generators).[1] Since the jet engine gearbox speed varies from idle to full power, this creates the need for a constant speed drive (CSD). The CSD takes the variable speed output of the accessory drive gearbox and hydro-mechanically produces a constant output RPM.[2][3]
Different systems have been used to control the alternator speed. Modern designs are mostly hydrokinetic, but early designs often took advantage of thebleed air available from the engines. Some of these were mostly mechanically powered, with an air turbine to provide a vernier speed adjustment. Others were purely turbine-driven.[4]
On aircraft such as theAirbus A310,Airbus A320 family,Airbus A320neo,Airbus A330,[5]Airbus A330neo,Airbus A340,[6]Boeing 737 Next Generation,747,757,767 and777, an integrated drive generator (IDG) is used.[7] This unit is simply a CSD and an oil cooled generator inside the same case.[8] Troubleshooting is simplified as this unit is theline-replaceable electrical generation unit on the engine.
Collins Aerospace (formerly UTC Aerospace Systems (formerlyHamilton Sundstrand)) is an American manufacturer of CSD and IDG units.
A variable-speed constant-frequency (VSCF) generator can be used to provide AC power using an electronictap converter.
Variable Frequency Starter Generator (VFSG) used primarily on the Boeing 787 are both used for electric start and electric generation.
An electronicPower inverter can take a variable frequency and voltage AC or variable voltage DC input, e.g. from apermanent magnet generator, and convert it to fixed RMS voltage and frequency AC.
