Coffee machine infusion group

Coffee machine infusion group comprising a closure piston and an infusion cylinder subjectable to a reversible movement between a position of engagement with said closure piston for the creation of an infusion chamber and a position of disengagement from said closure piston for the loading of a coffee powder load, said infusion group having an expulsion system of the spent coffee powder load from said infusion cylinder, said expulsion system having an expulsion piston displaceably housed in said infusion cylinder and a speed multiplier mechanism operatively connecting said infusion cylinder and said expulsion piston for their relative displacement between a receiving position of said coffee powder load into said infusion cylinder and an expelling position of said coffee powder load from said infusion cylinder, said speed multiplier mechanism comprises a push rod having a first end operatively connected to a rod of said expulsion piston and a second end pivoted to a support integrally fixed to said infusion cylinder or to said carrier, a first transmission element integral with said push rod and having an arc of teeth meshing with an arc of teeth of a second transmission element pivoted to said support.