An cooling system including an oil circulation circuit includes a first circuit including an electric oil pump that discharges oil as a coolant to be supplied to an inverter and respective motors, and an HV radiator that cools the oil to be supplied to the inverter and the respective motors, and a second circuit including a mechanical oil pump that discharges the oil to be supplied to a lubrication-required part without passing through the HV radiator.

There is provided a vertical multicylinder straight engine in which the temperature distribution of a plurality of cylinder barrels is made close to an even state. A cylinder jacket includes: a jacket inlet; a separated channel; a plurality of separated outlets; and heat dissipator channels for dissipating heat of the respective cylinder barrels to engine cooling water introduced through the separated outlets. The plurality of separated outlets include: a front-side separated outlet to a front-end barrel; a rear-side separated outlet to a rear-end barrel; and middle separated outlets to middle barrels between the front-end barrel and the rear-end barrel, and the jacket inlet is disposed so as to be contained within an entire middle barrel side area that is lateral to the middle barrels and has a front-rear length as long as a length from a front-most end to a rear-most end of the middle barrels.

The invention provides a single radiator cooling system for use in hybrid electric vehicles, the system comprising a surface in thermal communication with electronics, and subcooled boiling fluid contacting the surface. The invention also provides a single radiator method for simultaneously cooling electronics and an internal combustion engine in a hybrid electric vehicle, the method comprising separating a coolant fluid into a first portion and a second portion; directing the first portion to the electronics and the second portion to the internal combustion engine for a time sufficient to maintain the temperature of the electronics at or below 175 C.; combining the first and second portion to reestablish the coolant fluid; and treating the reestablished coolant fluid to the single radiator for a time sufficient to decrease the temperature of the reestablished coolant fluid to the temperature it had before separation.

An cooling system including an oil circulation circuit includes a first circuit including an electric oil pump that discharges oil as a coolant to be supplied to an inverter and respective motors, and an HV radiator that cools the oil to be supplied to the inverter and the respective motors, and a second circuit including a mechanical oil pump that discharges the oil to be supplied to a lubrication-required part without passing through the HV radiator.