Abstract

A drive gear is mounted for rotation in a plane parallel with the axis of rotation of the output member of the motor. The gear includes an annular series of beveled gear teeth in meshing engagement with beveled pinion teeth on the end of the motor output member. The drive gear includes a crank pin roller and an annular cam surface eccentric to the axis of rotation of the gear. The roller is received within a rectilinear slot in the plunger assembly thereby defining a scotch-yoke drive for reciprocating the plunger assembly. The plunger assembly includes planar cam follower formations engaged by the annular cam surface to provide an oscillating component of movement to the plunger assembly. The crank pin mounts a disk in eccentric relationship to the drive gear; this disk supports another crank pin and roller. A counterweight having a mass substantially the same as the plunger assembly has a rectilinear slot receiving the last-mentioned roller thereby constituting a second scotch-yoke drive for reciprocating the counterweight. The counterweight includes planar cam follower surfaces engaged with peripheral portions of the disk thereby imparting an oscillatory component to movement of the counterweight.