Oil supply system for an engine

A method for cooling a piston of an engine, comprising:

• controlling a position of a solenoid valve hydraulically coupled to a first inlet of a spool valve to operate a variable flow rate oil pump in either a low-pressure mode or a high-pressure mode based on engine speed and engine load, including controlling the position of the solenoid valve to operate the variable flow rate oil pump in the low-pressure mode irrespective of engine load if engine speed is below a lower limiting value, the solenoid valve permitting oil flow from an oil galley to the first inlet of the spool valve via a secondary feedback supply during the low-pressure mode and blocking oil flow from the oil galley to the first inlet of the spool valve during the high-pressure mode, a second inlet of the spool valve permanently hydraulically coupled with the oil galley via a primary feedback supply, and an outlet of the spool valve hydraulically coupled to an inlet of the variable flow rate oil pump, the solenoid valve having a default position wherein oil flow in the secondary feedback supply is blocked and the variable flow rate oil pump is operated in the high-pressure mode;
• pumping oil from the oil galley to a piston cooling jet via a pressure-operated valve when the variable flow rate oil pump is operating in the high-pressure mode, the piston cooling jet configured to supply the piston with oil to cool the piston;
• and
• pumping oil through the oil galley and blocking the piston cooling jet when the variable flow rate oil pump is operating in the low-pressure mode.

An oil supply system for a reciprocating piston internal combustion engine, the system comprising:

• an electronic control unit;
• an oil reservoir;
• a variable flow rate pump to supply oil at pressure from the reservoir to components including at least one piston cooling jet hydraulically coupled to an oil galley and requiring a supply of oil;
• a spool valve having an outlet hydraulically coupled to an inlet of the pump, a solenoid valve permitting oil flow from the oil galley to a first inlet of the spool valve, via a secondary feedback supply in a low-pressure mode of operation of the variable flow rate pump and blocking oil flow in the secondary feedback supply in a high-pressure mode of operation of the variable flow rate pump, and a second inlet of the spool valve permanently hydraulically coupled with the oil galley via a primary feedback supply;
• and
• at least one pressure-operated valve to supply oil from the oil galley to the at least one piston cooling jet, each pressure-operated valve coupled to one piston cooling jet and configured to open at a pre-defined valve opening pressure,
• wherein the variable flow rate pump is operable to supply oil in the low-pressure mode of operation at a first pre-defined pressure below the pre-defined valve opening pressure and to supply oil in the high-pressure mode of operation at a second pre-defined pressure above the pre-defined valve opening pressure,
• wherein the electronic control unit is operable to select either the low-pressure or the high-pressure mode of operation of the variable flow rate pump based upon a predefined relationship between engine speed and engine load, and
• wherein if engine speed is below a lower limiting value, the low-pressure mode of operation of the variable flow rate pump is selected irrespective of engine load.