Door holder-closer having a control signal operated hold-open function and a mechanical override facility

A door holder-closer having a control signal operated hold-open function and a mechanical override facility, said door holder-closer being adapted to hold a door in any desired open position to which it is moved from a closed position and comprising a housing for mounting on one of a door and fixed structure adjacent thereto;

• a unit for generating a closing force contained in said housing;
• a drive axle extending from said unit out of said housing;
• lever means connectable between said drive axle and the other one of said door and said fixed structure;
• a mechanically overridable clutch disposed between said lever means and said drive axle for transmitting torque from said lever means to said drive axle to rotate the same on opening of said door, whereby to energize said unit;
• and a blocking device for blocking said unit to generate a holding force and prevent said unit from moving said door in the door closing direction, said blocking device being capable of being switched in and out by control signals;
• wherein said overridable clutch between said lever means and said drive axle comprises first and second interengaging threaded elements, a first abutment provided on said first threaded element, a second abutment provided on said second threaded element and confronting said first abutment, wherein, in said open position of said door, said confronting first and second abutments are in frictional engagement with one another, thus generating a frictional locking force and frictionally locking said lever means to said drive axle;
• wherein said threaded elements are handed so that manual forced closing movement of said door from a said open position to said closed position overcomes said frictional engagement without overcoming said holding force and thus produces relative rotation of said first and second threaded elements and separation of said confronting first and second abutments, thus permitting manual relative rotation between said drive axle and said lever means to thereby manually move the door toward said closed position, and wherein said frictional locking force is less than said holding force.