System and method to reduce viscous losses of electric vehicle
Systems and methods for cooling and delivering oil for an electric vehicle are described. In one example, viscosity of oil and resistance to oil flow of an oil circuit reduce oil flow through a cooling circuit so as to reduce powertrain losses that may be related to oil viscosity. At higher temperatures, the viscosity of oil allows the oil to flow through the cooling circuit and lower a temperature of an electric machine.
1 . A system, comprising:
an electric machine;
a gearbox mechanically coupled to the electric machine and wheels of a vehicle, the gearbox including lubricating passages or conduits;
an oil sump configured to receive returned oil from the electric machine and the gearbox;
an oil pump configured to draw oil from the oil sump;
an oil cooler; and
a first oil passage or conduit extending from the oil pump to a second oil passage or conduit that extends to the oil cooler, the first oil passage or conduit also extending to a third oil passage or conduit that extends to the lubricating passages or conduits, the first oil passage or conduit extending from the oil pump, the second oil passage or conduit, and the third oil passage or conduit, not including control valves to control a flow of oil to the lubricating passages and the electric machine, wherein the oil cooler and the lubricating passages or conduits of the gearbox are configured such that oil flow is passively directed through one or both of the oil cooler and the lubricating passages or conduits based on a first flow resistance of the oil cooler, a second flow resistance of the lubricating passages or conduits, and oil viscosity.
2 . The system of claim 1 , the fourth oil passage or conduit not extending to the lubricating passages or conduits, wherein the fourth oil passage or conduit extends between the oil cooler and the electric machine without any connecting or intervening passages or components, and a fifth oil passage or conduit extending from the electric machine to the oil sump.
3 . The system of claim 1 , wherein oil flow through the oil cooler is substantially prevented when oil temperature is below a threshold temperature due to a combination of oil viscosity of the oil and the first flow resistance of the oil cooler.
4 . The system of claim 2 , further comprising a sixth oil passage or conduit extending from the lubricating passages to the oil sump.
5 . The system of claim 1 , wherein, when the temperature of the oil is above the threshold, the oil flows through the second and third passages or conduits.
6 . The system of claim 1 , wherein the oil pump is one of mechanically driven and electrically driven.
7 . The system of claim 6 , further comprising a controller including executable instructions stored in non-transitory memory that cause the controller to activate the oil pump.
8 . The system of claim 7 , further comprising additional instructions that cause the controller to adjust a speed of the oil pump in response to an oil temperature.
9 . A method for an electric powertrain, comprising:
pumping oil from a sump through a passage or conduit that extends from an oil pump to a second passage or conduit and a third passage or conduit, the second passage or conduit extending to an oil cooler, the third passage or conduit extending to lubrication circuits of a gearbox, the gearbox mechanically coupled to an electric machine, and an absence of control valves positioned along the passage or conduit, the second passage or conduit, and the third passage or conduit, wherein direction of oil flow is controlled by a combination of oil viscosity due to oil temperature and a resistance to oil flow of the oil cooler.
10 . The method of claim 9 , further comprising returning oil from the gearbox to the sump.
11 . The method of claim 10 , further comprising flowing oil from the oil cooler to the electric machine.
12 . The method of claim 9 , wherein oil flows through both the oil cooler and the lubrication circuits when oil temperature is above a threshold temperature, and wherein oil flow through the oil cooler is substantially prevented when oil temperature is below the threshold temperature.
13 . The method of claim 2 , further comprising returning oil from the electric machine to the sump.
14 . The method of claim 9 , further comprising activating the oil pump via a controller.
15 . The method of claim 14 , further comprising adjusting a speed of the oil pump via the controller in response to oil temperature and electric machine temperature.
16 . A system, comprising:
an electric machine;
a gearbox mechanically coupled to the electric machine and wheels of a vehicle, the gearbox including lubricating passages or conduits;
an oil sump configured to receive returned oil from the electric machine and the gearbox;
an oil pump configured to draw oil from the oil sump;
an oil cooler;
an oil passage or conduit extending from the oil pump to a second oil passage or conduit that extends to the oil cooler, the oil passage or conduit also extending to a third oil passage or conduit that extends to the lubricating passages or conduits, the oil passage or conduit extending from the oil pump, the second oil passage or conduit, and the third oil passage or conduit, not including control valves to control a flow of oil to the lubricating passages and the electric machine;
a first oil circuit including the oil cooler and the electric machine; and
a second oil circuit including the lubricating passages, wherein flow of oil through the first oil circuit is substantially prevented when oil temperature is below the threshold temperature due to a combination of a flow resistance of the first oil circuit relative to the second circuit and a viscosity of the oil when below the threshold temperature.
17 . The system of claim 16 , wherein oil flows through both the first oil circuit and the second oil circuit when oil temperature is above the threshold.
18 . The system of claim 17 , wherein the oil pump is mechanically driven.
19 . The system of claim 17 , wherein the oil pump is electrically driven.
20 . The system of claim 16 , further comprising a controller, the controller including executable instructions stored in non-transitory memory that cause the controller to adjust a speed of the oil pump in response to an oil temperature and an electric machine temperature.