Downhole tool comprising a rotating part with a torque limiting coupling

Downhole tool (100) for use in a petroleum well, the downhole tool (100) comprising a first part (110) comprising a driving unit (8), and second part (120) comprising a driven unit (9), wherein the driving unit (8) is configured for driving the driven unit (9), characterised in that the downhole tool (100) further comprises a coupling unit (1) having an input side (S1) coupled with the driving unit (8) and an output side (S2) coupled with the driven unit (9), wherein the driving unit (8) is configured for driving the driven unit (9) via the coupling unit (1), wherein the coupling unit (1) comprises a torque limiting coupling having a first operational mode wherein the coupling unit (1) transfers all torque from the input side (S1) to the output side (S2), the coupling unit (1) further having a second operational mode, wherein the coupling unit (1) slips such that less torque is transferred from the input side (S1) to the output side (S2), wherein the second operational mode is automatically activated when the torque load on the input side exceeds a predefined level, wherein the first operational mode is automatically activated when a torque load on the input side reduces to a level below a further predefined level, wherein the coupling unit (1) comprises a displacement pump (2), wherein the displacement pump 2 is activated by opening of a pressure-limitation valve (4) for facilitating slipping of the coupling unit (1) when the coupling unit (1) is switched to the second operational mode, and wherein the displacement pump (2) is deactivated by closing of the pressure-limitation valve (4), for locking the coupling unit (1) when the coupling unit (1) is switched to the first operational mode;

• and wherein the torque-limiting coupling comprises a housing (22) and the displacement pump (2) provided within the housing (22), wherein said housing (22) comprises:
• a rotor (21), wherein said rotor (21) is attached to a first connection device (5) that is axially rotatable around a rotation axis (51);
• an inlet (24) connected to a fluid reservoir (6);
• a pressure chamber (3) connected to an outlet (23);
• and
• a pressure limitation valve (4), wherein said housing (22) is attached to a second connection device (5′) that is rotatable around a rotation axis (51′);
• and
• wherein said pressure limitation valve (4) is provided between said pressure chamber (3) of said displacement pump (2) and said outlet (23).