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, also called an ''electric generator'', ''electrical generator'', and ''electromagnetic generator'' is an electromechanical device that converts mechanical energy to electrical energy for use in an extern ...

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

gas turbine A gas turbine or gas turbine engine is a type of Internal combustion engine#Continuous combustion, continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas gene ...

engines, such as aircraft

jet engine A jet engine is a type of reaction engine, discharging a fast-moving jet (fluid), jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition may include Rocket engine, rocket, Pump-jet, water jet, and ...

s. 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 An airliner is a type of airplane for transporting passengers and air cargo. Such aircraft are most often operated by airlines. The modern and most common variant of the airliner is a long, tube shaped, and jet powered aircraft. The largest ...

and

military aircraft A military aircraft is any Fixed-wing aircraft, fixed-wing or rotorcraft, rotary-wing aircraft that is operated by a legal or insurrectionary military of any type. Some military aircraft engage directly in aerial warfare, while others take on su ...

jet engines to drive the

alternating current Alternating current (AC) is an electric current that 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 w ...

(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 in aerospace engineering 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 (ASCPC) valves bleed air from low or high stage engine ...

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, Aircraft design process, designed and manufactured by Airbus Industrie GIE, then a consortium of European aerospace manufacturers. Airbus had identified a demand for an aircraft smaller than the Airbus ...

, Airbus A320 family,

Airbus A320neo The Airbus A320neo family is an incremental development of the A320 family of narrow-body airliners produced by Airbus. The A320neo family (''neo'' being Greek for "new", as well as an acronym for "new engine option") is based on the Airbus A3 ...

Airbus A330 The Airbus A330 is a wide-body airliner developed and produced by Airbus. Airbus began developing larger A300 derivatives in the mid–1970s, giving rise to the A330 twinjet as well as the Airbus A340 quadjet, and launched both designs along ...

Airbus A330neo The Airbus A330neo ("neo" for " New Engine Option") is a wide-body airliner developed by Airbus from the original Airbus A330 (now A330''ceo'' – "Current Engine Option"). A new version with modern engines comparable with those developed fo ...

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

Boeing 737 Next Generation The Boeing 737 Next Generation, commonly abbreviated as 737NG, or 737 Next Gen, is a twinjet, twin-engine narrow-body aircraft produced by Boeing Commercial Airplanes. Launched in 1993 as the third-generation derivative of the Boeing 737, it ha ...

, 747, 757, 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 Collins Aerospace is an American technology company that is one of the world's largest suppliers of aerospace and defense products. It was formed in 2018 from the merger of Rockwell Collins and UTC Aerospace Systems. Headquartered in Charlotte, ...

(formerly UTC Aerospace Systems (formerly Hamilton Sundstrand)) 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. An electronic Power inverter can take a variable frequency and voltage AC or variable voltage DC input, e.g. from a permanent magnet generator, and convert it to fixed RMS voltage and frequency AC.

References

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

Mechanism

Integrated drive generator

Manufacturers

Alternatives

See also

References