Vibratory drive unit

Claim 1

Rotary vibrator drive unit comprising a disc-like support member secured to a driven shaft for rotation therewith, an unbalanced mass slidably secured to the support member for outward radial movement under the influence of centrifugal force, said unbalanced mass being slotted with the slot enclosing the driven shaft, a bridging crossbar across the open end of the slot, a pair of spring housings secured to the support member in diametrically opposed parallel relationship, a first helical coil spring within each housing held between the crossbar and a flange at the end of its spring housing remote from the crossbar, each said first helical coil spring when the drive unit is stationary being partially compressed and urging the unbalanced mass toward the position of minimum unbalance, a second helical coil spring within and coaxial with each first coil spring and being of shorter length than the first coil spring, each said second coil spring being secured at one end to the crossbar and with its other end slidable over a spigot on said flange so that each said second coil spring engages between the unbalanced mass and the support member only when the unbalanced mass has moved radially outward a predetermined distance, a housing surrounding the unbalanced mass and coil springs, and a damping oil filling the housing.