Operating method for a hydraulic system of an automatic transmission

A method for operating a hydraulic system of an automatic transmission, the hydraulic system including a primary circuit (P), a secondary circuit (S), at least one gear pump (2, 21) and one valve unit (3), the gear pump (21) operable by an electric motor (22), the valve unit (3) arranged between the primary circuit (P) and the secondary circuit (S), the valve unit (3) controllable such that the primary circuit (P) and the secondary circuit (S) are connectable and disconnectable by the valve unit (3), a hydraulic resistance between the primary and secondary circuits (P, S) is changeable by the valve unit (3) when the primary circuit (P) and the secondary circuit (S) are connected, the method comprising:

• measuring an input current (I_22) of the electric motor;
• determining a defined primary pressure value (p_PE) for the primary circuit (P) based on the measured input current (I_22) of the electric motor (22);
• adjusting a primary pressure (p_P) of the primary circuit (P) to the defined primary pressure value (p_PE);
• calculating a target speed (n_Z) of the electric motor (22);
• and
• adjusting a secondary flow rate (Q_S) of the secondary circuit (S) to a target secondary flow rate (Q_SZ) by changing a speed (n) of the electric motor (22) to the calculated target speed (n_Z).