Coffee machine with proportional pre-infusion system

Coffee machine comprising:

• a filter holder suitable for containing at least one coffee dose;
• a dispensing unit suitable for receiving the filter holder;
• said dispensing unit being provided with dispensing nozzles suitable for sending a flow of hot water on the coffee dose contained in the filter holder;
• a water system provided with a pump to supply pressurized water to said dispensing nozzles of the dispensing unit;
• a heater disposed in said water system to heat the water to be supplied to the dispensing nozzles;
• a dispensing valve disposed in said water system between the heater and the dispensing nozzles to enable/disable the supply of hot water to said dispensing nozzles;
• a pre-infusion valve disposed in said water system upstream said dispensing valve;
• and
• a control unit comprising actuation means to actuate said pre-infusion valve;
• wherein said pre-infusion valve is a two-way electrovalve of programmable proportional type, comprising a shutter suitable for gradually opening and closing the communication between the two ways of the valve proportionally to a command signal sent by said actuation means;
• wherein the actuation means and the pre-infusion valve are configured in such a way to have:
• a dispensing time (Te) from the moment when the pre-infusion valve is opened to the moment when the pre-infusion valve is closed;
• an opening time (T1) from the moment when the pre-infusion valve starts opening to the moment when the pre-infusion valve is completely open;
• a maximum flow time (T2) in which the pre-infusion valve is completely open;
• and
• a closing time (T3) from the moment when the pre-infusion valve starts closing to the moment when the pre-infusion valve is completely closed;
• wherein the closing time (T1) is higher than ⅓ of the dispensing time (Te), the maximum flow time (T2) is lower than ⅓ of the dispensing time (Te), and the closing time (T2) is higher than ⅓ of the dispensing time (Te).