Turbocharger assembly with oil carry-over protection

A method for controlling oil leakage in an assembly, the assembly including:

• a first turbocharger including a first turbine and a first compressor,
• the first turbine being arranged in a turbine flowpath to be driven in rotation by an exhaust gas flowing at a variable flow rate through the turbine flowpath,
• the first compressor being arranged in a compressor flowpath to be driven in rotation by the first turbine via a first shaft to urge an intake gas to flow through the compressor flowpath;
• bearings supporting the first shaft for rotation of the first turbine and the first compressor, the bearings being supplied with oil via an oil flowpath at an oil pressure;
• a seal arranged between the oil flowpath and the compressor flowpath to resist leakage of the oil into the compressor flowpath, a seal pressure gradient being defined by a pressure of the compressor flowpath acting on the seal minus the oil pressure;
• flow control means operable to control a rotational speed of the first turbine and first compressor by controlling the flow of exhaust gas through the turbine flowpath;
• and
• a controller operatively coupled to the flow control means,
• the method comprising:
• identifying, via the controller, a minimum rotational speed of the first compressor to maintain the seal pressure gradient not less than a minimum pressure gradient value;
• and
• adjusting, via the controller, the flow control means to control the flow of exhaust gas through the turbine flowpath to maintain a rotational speed of the first compressor above the minimum rotational speed.