Watt's linkage

Watt's linkage

Watt's linkage (also known as the parallel linkage) is a type of mechanical linkage invented by James Watt (19 January 1736 – 25 August 1819) to constrain the movement of a steam engine piston in a straight line.

The idea of its genesis using links is contained in a letter he wrote to Matthew Boulton in June 1784.:"I have got a glimpse of a method of causing a piston rod to move up and down perpendicularly by only fixing it to a piece of iron upon the beam, without chains or perpendicular guides [...] and one of the most ingenious simple pieces of mechanics I have invented."

This linkage does not generate a true straight line motion, and indeed Watt did not claim it did so. In a letter to Boulton on 11th September 1784 he describes the linkage as follows.:"The convexities of the arches, lying in contrary directions, there is a certain point in the connecting-lever, which has very little sensible variation from a straight line."

Car suspension

The Watt's linkage is used in the rear axle of some car suspensions as an improvement over the Panhard rod, which was designed in the early twentieth century. Both methods intend to prevent relative sideway motion between the axle and body of the car. The Watt’s linkage however approximates a vertical straight line motion more closely.

It consists of two horizontal rods of equal length mounted at each side of the chassis. In between these two rods, a short vertical bar is connected. The center of this short vertical rod – the point which is constrained in a straight line motion - is mounted to the center of the axle. All pivoting points are free to rotate in a vertical plane.

In a way, the Watt’s linkage can be seen as two Panhard rods mounted opposite of each other. In Watt’s arrangement however, the opposing curved movements introduced by the pivoting Panhard rods are compensated by the short vertical rotating bar.

The Watt's linkage can also be used to prevent axle movement in the longitudinal direction of the car, this is however more common in racing suspension systems. This application usually involves two Watt's linkages on each side of the axle, mounted parallel to the driving direction.

ee also

External links

* [http://www.howround.com/ How round is your circle?] Contains a chapter explaining the history of Watt's linkage.
* [http://www.keveney.com/watt.html Watt Beam Engine]
* [http://historical.library.cornell.edu/cgi-bin/cul.math/docviewer?did=Kemp009&seq=19&frames=0&view=50 How to draw a straight line, by A.B. Kempe, B.A.]
* [http://kmoddl.library.cornell.edu/model.php?m=145 Lemniscoidal (figure 8 curved) linkage of the first kind by Watt]
* [http://kmoddl.library.cornell.edu/model.php?m=146 Lemniscoidal linkage of the second and third kind by Watt]
* [http://mw.concord.org/modeler1.3/mirror/mechanics/peaucellier.html A simulation] using the Molecular Workbench software

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Linkage (mechanical) — This article is about assemblies of links designed to manage forces and movement. For other uses, see Linkage. Variable stroke engine (Autocar Handbook, Ninth edition) A mechanical linkage is an assembly of bodies connected together to manage… …   Wikipedia

  • linkage — Any series of rods, yokes, levers, bars or links used to transmit motion from one unit to another. Also see center steering linkage gearchange linkage parallelogram steering linkage progressive linkage shifter linkage shift linkage steering… …   Dictionary of automotive terms

  • Watt steam engine — The Watt steam engine was the first type of steam engine to make use of steam at a pressure just above atmospheric to drive the piston helped by a partial vacuum. Improving on the design of the 1712 Newcomen engine, the Watt steam engine,… …   Wikipedia

  • watt linkage — A suspension linkage which has three bars to locate the De Dion or live axle. There are two usual methods for arranging a Watt linkage: frame to pivot on axle housing to frame or axle to pivot on frame to axle. In either arrangement, this link… …   Dictionary of automotive terms

  • James Watt — Infobox Person name = James Watt caption = Inventor and Mechanical Engineer birth date = birth date|1736|1|19 birth place = Greenock, Firth of Clyde, Scotland, Kingdom of Great Britain death date = death date |1819|8|25| Although a number of… …   Wikipedia

  • Chebyshev linkage — The Chebyshev linkage is a mechanical linkage that converts rotational motion to approximate straight line motion. It was invented by the 19th century mathematician Pafnuty Chebyshev who studied theoretical problems in kinematic mechanisms. One… …   Wikipedia

  • Sarrus linkage — The Sarrus linkage, invented in 1853 by Pierre Frédéric Sarrus, is a mechanical linkage to convert a limited circular motion to a linear motion without reference guideways. The linkage uses two perpendicular hinged rectangular plates positioned… …   Wikipedia

  • Scott Russell linkage — A Scott Russell linkage converts linear motion, to (almost) linear motion in a line perpendicular to the input. These linkages are often used in front wheel drive vehicles with solid rear axles to control lateral movement, as they do not share… …   Wikipedia

  • Cognate linkage — In Kinematics, cognate linkages are linkages that ensure the same input output relationship or coupler curve geometry, while being dimensionally dissimilar. In case of four bar linkage coupler cognates, the Roberts–Chebychev theorem states that… …   Wikipedia

  • Mechanism (engineering) — A mechanism is a device designed to transform input forces and movement into a desired set of output forces and movement. Mechanisms generally consist of moving components such as gears and gear trains, belt and chain drives, cam and follower… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.