Vehicle door latches and locking mechanism

A vehicle door latch assembly, comprising:

• (a) a latch bolt for interaction with a striker formation of an associated door frame in use, the bolt in a latched position keeping the door fully closed;
• (b) retention means cooperating with the bolt to secure it at the latched position;
• (c) release means connected to interior and exterior door handles or other operating means in use to actuate the retention means for freeing the bolt to allow the door to open, said release means including a locking dog displaceable between an active position at which it drivingly connects said operating means for movement of the retention means and an inactive position at which the operating means is disconnected from the retention means;
• (d) locking mechanism comprising locking means which when in a locked condition disables the release means to prevent actuation of the retention means by attempted operation of at least the exterior door handle or other exterior operating means in use, said locking means including:
• (i) a rotatably driven worm shaft and a worm nut in threaded engagement therewith, displacement of the nut along the shaft carrying said dog between the active and inactive positions;
• (ii) a crank element fulcrummed for selective angular movement about a first axis to a first angular position at which the locking means is not in the locked condition and to second and third angular positions at both of which the locking means is in the locked condition, and
• (iii) a linkage having pivotal connection to the crank element on a second axis spaced from the first axis for effecting said angular movement of the crank element manually;
• and
• (e) deadlocking means selectively operable to cause the crank element to take up the third angular position, the first and second axes being substantially in line with the direction of operative movement of the linkage at the latter position whereby the linkage cannot be used to effect angular movement of the crank element from that position to return the locking means to unlocked condition.