Editing Constant-velocity joint (section)

=== Thompson joints ===
[[File:TCVJ.jpg|thumb|A diagram of a Thompson coupling]]
The Thompson joint (also known as a ''Thompson coupling'') assembles two cardan joints within each other to eliminate the intermediate shaft.<ref>{{cite patent |country=US |inventor=Glenn Thompson |title=CONSTANT VELOCITY COUPLING AND
CONTROL SYSTEM THEREFOR |number=US20040106458A1 |pridate=2001-03-26 |pubdate=2004-06-03 |gdate=2006-12-05 |status=patent}}</ref>  A control yoke is added to keep the input and output shafts aligned. The control yoke uses a spherical [[pantograph]] [[scissor mechanism]] to bisect the angle between the input and output shafts and to maintain the joints at a relative phase angle of zero. The alignment ensures constant angular velocity at all joint angles. Eliminating the intermediate shaft and keeping the input shafts aligned in the homokinetic plane greatly reduces the induced [[shear stress]]es and [[vibration]] inherent in [[Universal joint#Double Cardan shaft|double cardan shafts]].<ref name="Sopanen">{{cite web | url = http://www.ee.lut.fi/static/fi/lab/sahkokaytot/sameko/Cardan_Sameko.pdf | title = Studies on Torsion Vibration of a Double Cardan Joint Driveline | last = Sopanen | first = Jussi | year = 1996 | access-date = 2008-01-22 | url-status = dead | archive-url = https://web.archive.org/web/20090205135715/http://www.ee.lut.fi/static/fi/lab/sahkokaytot/sameko/Cardan_Sameko.pdf | archive-date = 2009-02-05 }}</ref><ref name = "Sheu">{{cite web | url = http://cat.inist.fr/?aModele=afficheN&cpsidt=3004428| title = Modelling and analysis of the Intermediate Shaft Between Two Universal Joints| last = Sheu| first = P| date = 2003-02-01| access-date = 2008-01-22 }}</ref><ref name="tcvj in action video">{{cite web|title=The Thompson Coupling Joint mechanism in action|url=https://www.youtube.com/watch?v=-tmvBwVPcSs|publisher=Thompson Couplings|access-date=24 September 2011}}</ref> While the geometric configuration does not maintain constant velocity for the control yoke that aligns the cardan joints, the control yoke has minimal inertia and generates little vibration. Continuous use of a standard Thompson coupling at a straight-through, zero-degree angle will cause excessive wear and damage to the joint; a minimum offset of 2 degrees between the input and output shafts is needed to reduce control yoke wear.<ref>{{cite web|title=Extra Length 500Nm TCVJ|url=http://www.thompsoncouplings.com/500Nm-AE-TCVJ-EL/Extra-Length-500Nm-TCVJ%28R%29/pd.php|publisher=Thompson Couplings, Ltd.|access-date=25 September 2011|quote=Special Instructions: Continuous operation of the TCVJ coupling at 0 degrees is not recommended as this will cause excessive wear on bearings and cause damage to the coupling. For maximum efficiency and life of the TCVJ coupling, a minimum operating angle of 2.0 degrees is recommended.|archive-url=https://web.archive.org/web/20111003234311/http://www.thompsoncouplings.com/500Nm-AE-TCVJ-EL/Extra-Length-500Nm-TCVJ%28R%29/pd.php|archive-date=3 October 2011|url-status=dead}}</ref> Modifying the input and output yokes so that they are not precisely normal to their respective shafts can alter or eliminate the "disallowed" angles.<ref>{{cite web |url=http://www.pattakon.com/pattakonPatDan.htm |title=PatDan and PatCVJ Constant Velocity Joints |access-date=2012-07-26 |author=pattakon.com}}</ref>

The novel feature of the coupling is the method for geometrically constraining the pair of cardan joints within the assembly by using, for example, a spherical four bar scissors linkage (spherical pantograph) and it is the first coupling to have this combination of properties.<ref name = "Bowman">{{cite web | url = http://www.centralwesterndaily.com.au/news/local/news/general/an-invention-to-drive-fuel-costs-down/191341.aspx | title = An invention to drive fuel costs down| publisher = yourguide.com.au | last = Bowman | first = Rebecca| date = 2006-08-03 | access-date = 2007-02-13 }}</ref>