Detained key assembly

Abstract

A deadlock of the customary type for locking and unlocking a dead bolt is equipped with a conventional cylinder having a cylinder plug rotating within it, the cylinder plug carrying pin chambers aligned with pin chambers in the cylinder for reception of pin tumblers when shifted in position by cut irregularities on the edge of the key. With chambers in alignment an appropriate key inserted in the keyway shifts the pin tumblers to positions coincident with a shear line to permit rotation of the plug to either locked or unlocked position. Unless the chambers are in alignment, the tumblers cannot shift and the key can be neither inserted nor withdrawn. For preventing withdrawal of the key on, for example, the inside of the door, when the dead bolt is locked, there is a detained key mechanism. The mechanism makes use of one cam element on the cylinder plug moving with relation to another cam element on the cylinder so that with cam elements released in locked position of the dead bolt, a slight axial shift of the cylinder plug is permitted sufficient to misalign the chambers and prohibit withdrawal of the key. When the plug is returned to unlocked position, engagement of the cams prevents the slight axial shift of the cylinder plug thereby holding the chambers in alignment so that the pin tumblers can shift and the key can be withdrawn.