Use of dynamic pressure to control fluid bleed system

A method of controlling flow of fluid in a hydraulic circuit of a drive unit comprising:

• providing a drive unit having:
• a housing including a central portion and a gearbox portion separate from the central portion;
• at least one of an electric motor or a heat exchanger supported in the central portion of the housing;
• a gearbox having rotating components supported in a gearbox portion of the housing;
• an oil circuit in fluid communication with the gearbox portion of the housing for circulating oil to and from at least one of the electric motor or the heat exchanger in the central portion of the housing in response to dynamic pressure generated by the rotating components of the gearbox when in operation;
• and
• a bleed passage connecting the oil circuit in the central portion of the housing to the gearbox portion of the housing;
• and
• operating the rotating components of the gearbox to generate a dynamic pressure in the gearbox portion of the housing to restrict flow of oil through the bleed passage from the oil circuit to the gearbox portion of the housing.

A drive unit comprising:

• a housing;
• a gearbox having rotating components supported in the gearbox portion of the housing;
• an oil circuit in fluid communication with the gearbox portion of the housing for circulating oil in response to dynamic pressure generated by the rotating components of the gearbox when in operation;
• and
• a bleed passage connecting the oil circuit to the gearbox portion of the housing;
• wherein dynamic pressure in the gearbox portion of the housing generated by the rotating components when in operation restricts flow of oil through the bleed passage from the oil circuit to the gearbox portion of the housing;
• wherein static pressure in the gearbox portion of the housing when the gearbox is not in operation permits flow of oil from the oil circuit to the gearbox portion of the housing;
• wherein the gearbox portion of the housing includes a sump;
• wherein the oil circuit is connected to the gearbox portion of the housing for the supply and return of oil above the sump and the bleed passage is connected to the sump;
• wherein the housing includes a central portion containing at least one of a heat exchanger or a motor, and the oil circuit circulates oil through at least one of the heat exchanger or the motor;
• and
• further comprising a gasket between the gearbox portion of the housing and the central portion of the housing, wherein the bleed passage comprises a hole in the gasket.