Watt's linkage

The Watt mechanism is composed of the Watt's linkage and the Watt parallelogram. This functional separation has been blurred for a long time, so that the Watt mechanism has been referred to as Watt parallelogram in numerous previous publications.

The Watts link is a machine element for converting a rotational swing motion in the plane in an approximate straight-line motion. The function of the watt parallelogram is the scaling of the movement of the Watt linkage.

Historical derivation

To increase the power of the steam engines he designed were James Watt was looking for ways to successively flow through the cylinders of his machine from both sides with steam in order to produce such an active upward movement of the cylinder next to the then usual active downward movement of the cylinder can. One speaks of a double-acting cylinder. Required for this purpose watts a rigid coupling of the cylinder with the balancing; the usual coupling by means of a chain could only transmit downward pulling forces of the cylinder. Invented by Watt 1784 watts mechanism includes the so-called Watts linkage that adjusts the rotation of the balanciers the rectilinear movement of the cylinder. This usually requires a size adjustment: The Watt parallelogram scales the motion of the Watt's linkage such that the piston rod of the machine with about a fixed pivot point can be connected oscillating back and forth balancing.

James Watt wrote about his invention: " Although I do not care about fame, I 'm more proud of than any invention that I have done on the parallel movement. "

Operation

The Watt's parallelogram consists of two coupled components, the Watt's linkage and the parallelogram.

The Watt's linkage

The Watt's linkage is the actual mechanism which converts the movement of a point on a circular arc portion in a movement on a lemniscate. In some industries where the Watt linkage is therefore also known as Lemniskatenlenker. For small deflections the path of the lemniscate is approximately straight.

In the left diagram, the Watt linkage consists only of the two fixed points A and G, the two levers AB and EC, which can rotate in A and G, and the lever BE, to its endpoints rotatable (!) And the above two levers is connected. When the lever is rotated back and forth AB to point F is moved up and down almost on a straight line.

The right diagram shows the movement of a Watt linkage without the parallelogram. Here the endpoints of L1 and L3 on circular orbits, the point P move along a lemniscate.

Other mechanical designs that implement a rotational swing motion into linear motion, are the Inversor of Peaucellier and the Chebyshev - parallelogram.

The parallelogram

The parallelogram is formed in the left diagram of the points BCDE, where all four corners are rotatable joints. It has the function of a pantograph - as the points A, F, and D are in the appropriate length from a CD to a straight line and the distance from A to D is always proportional to the distance from A to F, thus performs D the same movement as F, only " magnified ". When F is moved to a ( nearly ) straight line, then that is also D - the point, which is connected to the piston H.

To operate a machine, the parallelogram would not strictly necessary - you could connect the rod, which begins on the piston H, directly with F. But that would mean that the piston stroke would be much smaller, or to achieve the same stroke that would have to walk right points B, E and G in particular much more night, which would significantly increase the space requirements of the machine.

The implementation of the movement by the Watt's linkage and the magnification of the stroke by means of a parallelogram, are two independent mechanisms, which may also be used separately.

Applications

The invention worked very quickly on the technology of the steam engine addition, since the conversion of movement types is quite crucial. For example, the steering mechanism, which is an essential part of the steering in any modern automobile, originated in Watt's parallelogram.

The Watts link (without the parallelogram ) is used in some cars with live axle, to prevent sideways movement of the axle. The vertical movement of the axis corresponds to a straight line, much better than, for example when using a Panhard rod.

Watt's linkage on a rear axle (Ford Ranger EV, 1998).

The same animated.

Under the name Lemniskatenlenker the Watt's linkage is used in rail vehicles in order to prevent movement of the wheel axles in the longitudinal direction of the train.

Watt's linkage on a bogie.

Jakobs truck Odakyu Electric Railway Type 7000th