A constant speed drive (CSD) also known as a constant speed generator, is a type of transmission 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, typically

electrical generator In electricity generation, a generator is a device that converts motive power (mechanical energy) or fuel-based power ( chemical energy) into electric power for use in an external circuit. Sources of mechanical energy include steam turbines, g ...

s, that require a constant input speed. The term is most commonly applied to hydraulic transmissions found on the

accessory drive The accessory drive is a gearbox that forms part of a gas turbine engine. Although not part of the engine's core, it drives the accessories, fuel pumps, etc., that are otherwise essential for the operation of the engine or the aircraft on which i ...

s of

gas turbine A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directio ...

engines, such as aircraft jet engines. On modern aircraft, the CSD is often combined with a generator into a single unit known as an integrated drive generator (IDG).

Mechanism

CSDs are mainly used on airliner and

military aircraft A military aircraft is any fixed-wing or rotary-wing aircraft that is operated by a legal or insurrectionary armed service of any type. Military aircraft can be either combat or non-combat: * Combat aircraft are designed to destroy enemy equi ...

jet engines to drive the

alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...

(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). 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. Different systems have been used to control the alternator speed. Modern designs are mostly hydrokinetic, but early designs often took advantage of the

bleed air Bleed air is compressed air taken from the compressor stage of a gas turbine upstream of its fuel-burning sections. Automatic air supply and cabin pressure controller (ASCPCs) valves bleed air from high or low stage engine compressor sections. Lo ...

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.

Integrated drive generator

On aircraft such as the

Airbus A310 The Airbus A310 is a wide-body aircraft, designed and manufactured by Airbus Industrie, then a consortium of European aerospace manufacturers. Airbus had identified a demand for an aircraft smaller than the A300, the first twin-jet wide-bod ...

Airbus A320 family The Airbus A320 family is a series of Narrow-body aircraft, narrow-body airliners developed and produced by Airbus. The A320 was launched in March 1984, Maiden flight, first flew on 22 February 1987, and was introduced in April 1988 by Air F ...

, Airbus A320neo,

Airbus A330 The Airbus A330 is a wide-body aircraft developed and produced by Airbus. Airbus conceived several derivatives of the A300, its first airliner in the mid-1970s. Then the company began development on the A330 twinjet in parallel with the A340 ...

, Airbus A330neo,

Airbus A340 The Airbus A340 is a long-range, wide-body passenger airliner that was developed and produced by Airbus. In the mid-1970s, Airbus conceived several derivatives of the A300, its first airliner, and developed the A340 quadjet in parallel wit ...

Boeing 737 Next Generation The Boeing 737 Next Generation, commonly abbreviated as 737NG, or 737 Next Gen, is a narrow-body aircraft powered by two jet engines and produced by Boeing Commercial Airplanes. Launched in 1993 as the third generation derivative of the Boeing ...

, 747,

757 757 may refer to: * Boeing 757: a narrow-body airliner * AD 757: a year * 757 BC: a year * 757 (number): a number * Area code 757 Image:Area code 757.png, The area colored red indicates the southeast corner of Virginia served by area code 757 po ...

, 767 and 777, an integrated drive generator (IDG) is used. This unit is simply a CSD and an oil cooled generator inside the same case. Troubleshooting is simplified as this unit is the line-replaceable electrical generation unit on the engine.

Manufacturers

Collins Aerospace (formerly UTC Aerospace Systems (formerly

Hamilton Sundstrand Hamilton Sundstrand was an American globally active corporation that manufactured and supported aerospace and industrial products for worldwide markets. A subsidiary of United Technologies Corporation, it was headquartered in Windsor Locks, Con ...

)) is an American manufacturer of CSD and IDG units.

Alternatives

A variable-speed constant-frequency (VSCF) generator can be used to provide AC power using an electronic tap converter. Variable Frequency Starter Generator (VFSG) used primarily on the Boeing 787 are both used for electric start and electric generation.

References

{{Aircraft gas turbine engine components Jet engine technology Aircraft components Aerospace engineering Vehicle technology

Mechanism

Integrated drive generator

Manufacturers

Alternatives

See also

References