A hydraulic system of a power transmission, comprising:
- a reservoir;
- a pump driven to supply an operating liquid from the reservoir;
- a first branch and a second branch starting from a junction point;
- the first branch configured to perform a cooling and/or lubricating function on a part of the power transmission;
- the second branch ending at a hydraulic actuator to perform an actuating function;
- control valves controlled by an electronic control unit to manage the operating liquid supplied by said pump;
- characterized in that said control valves comprise:
- a first control valve arranged along said first branch;
- a second control valve arranged along said second branch;
- wherein each of said first control valve and said second control valve comprises:
- a first port connected to said junction point;
- a second port connected to said reservoir;
- a third port;
- the third port of said first control valve being connected so as to direct the operating liquid towards the part to be cooled/lubricated;
- the third port of said second control valve communicating with a chamber of said hydraulic actuator for pressurizing said chamber;
- a selector body which is movable, in response to an electrical control signal, between a first position and at least a second position, wherein
- a) in the first position, the first port communicates with the third port;
- and
- b) in the second position, the first port is closed, and the second port communicates with the third port,
- wherein each of said first control valve and said second control valve further comprises a fourth port;
- the fourth port of said first control valve being disconnected or being in communication with said reservoir;
- the fourth port of said second control valve communicating with a further chamber of said hydraulic actuator for pressurizing said further chamber;
- wherein, in the second position, the second port communicates with the third port and with the fourth port;
- and wherein the selector body is movable also in a third position, in which the first port communicates with the fourth port, and the second port communicates with the third port-(A).