Adjustment mechanism and adjustment device comprising such adjustment mechanism

An adjustment mechanism for an adjustment device, the adjustment mechanism comprising a main worm gear wheel held in an injection molded plastic housing for rotation relative to each other about a main axis of the worm gear wheel, the main worm gear wheel being provided with a hollow central axial passage and the housing provided with at least one opening that is axially aligned with the central axial passage to allow a shaft to extend via the opening through the housing into the central axial passage and to be in supporting engagement with the main gear, the adjustment mechanism further comprising a main worm having at least one circumferential spiral tooth in intermeshing arrangement with teeth on the circumference of the main worm gear wheel, the main worm being held in the housing for rotation about a main axis of the main worm, and being arranged to be driven to rotation relative to the housing about its main worm axis via a drive train powered by an electric motor held in the housing. A number of stiffeners is provided between the housing and the main worm gear wheel and/or the main worm to lock the intermeshing arrangement of the teeth under torque that is applied between main worm gear and housing external to the drive.