Speed reducer for a wiper mechanism, having a housing closed by a cover

A speed reducer comprising a hollow casing and, in said casing, a toothed wheel, means defining an axis of rotation and mounting the toothed wheel for rotation about said axis, a crank pin carried by the toothed wheel for free rotation and axial movement, the crank pin extending axially and being eccentric with respect to said axis of rotation, an output shaft rotatable in the casing, and a crank and connecting rod system coupling the crank pin to the output shaft such that the crank for converting continuous rotary motion of the toothed wheel to alternating rotary motion of the output shaft such that the crank pin moves in a circular path about the axis of rotation of the toothed wheel, the speed reducer further including a cover closing said casing and having an inner face directed into the casing, the cover having at least one flat thickened portion arranged on its said inner face and being of a material having a low coefficient of friction, said thickened portion extending over the whole circular path of the crank pin about said axis of rotation of the toothed wheel.