Page:The Kinematics of Machinery.djvu/491

 DISENGAGING GEAR. 4C9

have a distinct general idea of the alterations thus occurring in the kinematic chain, in order thoroughly to understand the means by which those alterations are effected. We shall examine some examples of the methods commonly used.

One method very frequently adopted is the separation of the elements of an existing pair, so that the pairing between them may be dissolved. Friction wheels, moved a small distance away from each other, belt-trains in which the belt can be loosened

FIG. 338.

FIG. 837.

FIG. 339.

by moving a tightening pulley (Fig. 337), or by throwing it off one or both of the drums, spur-wheels which can be moved out of gear either axially (Fig. 338) or radially (Fig. 339) are all examples of this method. When the pairing is dissolved, the motion of the driven link necessarily ceases, no matter whether or not that of the driving-link continues. Engagement, or " throwing into gear," is simply the re-union or re-pairing of the separated elements.

Loose couplings (p. 445) or clutches are another form of dis- engaging gear. The most common form of this is the claw clutch