Constant speed drive
{{Short description|Type of gearbox used on jet engines}}
{{Use dmy dates|date=October 2015}}
File:Constant Speed Drive for Boeing 727, Sundstrand Corporation - Museum of Science and Industry (Chicago) - DSC06323.JPG, made by Sundstrand Corporation]]
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 generators, that require a constant input speed.
The term is most commonly applied to hydraulic transmissions found in the accessory drives of gas turbine 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 jet engines to drive the alternating 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).{{cite web
|url=https://www.angelfire.com/ct3/ctenning/electrical_essays/777elecpwr/777_design.html|title=Designing the 777 Electrical Power System|author=Carl Tenning|access-date=10 August 2015
}} 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.{{cite web
|url=http://www.k-makris.gr/AircraftComponents/CSD/C.S.D.htm|title=CSD|access-date=10 August 2015
|archive-url=https://web.archive.org/web/20100731084928/http://www.k-makris.gr/AircraftComponents/CSD/C.S.D.htm
|archive-date=2010-07-31
|url-status=dead
|url=http://www.freepatentsonline.com/4310768.html|title=Constant speed drive – Rolls-Royce Limited|access-date=10 August 2015
}}
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 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.{{Cite journal
|title=Accessory Power – Constant speed drives and starters
|journal=Flight International
|date=16 September 1960
|pages=460–461
|url=https://www.flightglobal.com/pdfarchive/view/1960/1960%20-%201967.html
}}
Integrated drive generator
On aircraft such as the Airbus A310, Airbus A320 family, Airbus A320neo, Airbus A330,{{cite web|url=http://www.smartcockpit.com/aircraft-ressources/A330-Electrical.html|title=A330 Electrical|access-date=10 August 2015}} Airbus A330neo, Airbus A340,{{cite web|url=http://www.smartcockpit.com/aircraft-ressources/FCOM_A340-Electrical.html|title=FCOM A340 Electrical|access-date=10 August 2015}} Boeing 737 Next Generation, 747, 757, 767 and 777, an integrated drive generator (IDG) is used.{{Cite book
|title=The Aircraft Gas Turbine Engine and its Operation
|author=Pratt & Whitney
|author-link=Pratt & Whitney
|publisher=United Technologies Corporation
|id=P&W 182408
|date=August 1988
|pages=3–45
}} This unit is simply a CSD and an oil cooled generator inside the same case.{{cite web|url=http://www.freepatentsonline.com/7064455.html|title=Fixed frequency electrical generation system and corresponding control procedure – Airbus France|access-date=10 August 2015}} 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)) 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.
See also
References
{{Commons category|Constant speed drives}}
{{Reflist}}
{{Aircraft gas turbine engine components}}
Category:Jet engine technology