Vehicles may use an engine oil system to lubricate and/or cool various components of an internal combustion engine. The oil system for an engine supplies oil from a reservoir, often referred to as a sump, to various components of the engine requiring a supply of oil, such as bearings, hydraulic valve mechanisms, and piston cooling jets.
As such, there may be many competing and overlapping demands on an engine oil system during vehicle operation. For example, different engine components may have different oil flow volume and oil pressure requirements. Further, the oil requirement for a given component may vary depending on operating conditions (e.g., engine load, engine temperature, etc.).
One approach to address the differing oil requirements of the various engine components includes the use of check valves and control valves to modify oil routing, oil pressure activation, etc. In another approach shown by Ducu in US 2005/0120982, a separate oil gallery, in addition to a main oil gallery, is provided for piston cooling. A single pump supplies oil to the main and the separate oil galleries. An electronic control valve controls the flow of oil into the separate gallery based on engine load and engine temperature. Oil supply to the separate gallery, and therefore, to the pistons, may be stopped by closing the control valve when engine temperature and/or engine loads are lower.
However the inventors herein have identified potential issues with the above approaches. For example, since a single oil pump is utilized to provide oil to different engine components, it has to be sized to meet high flow volumes for piston cooling. Thus, even though a separate gallery is used to supply oil to piston cooling jets, by using a single, oversized pump, there is an increase in power consumption and a loss in fuel economy. As another example, even though check valves and control valves may stop or reduce the flow to specific components, a single oil pump may continue to provide oil to a common oil gallery at a pressure requested by the highest requester, resulting in a loss of hydraulic power and a waste of energy.
The inventors herein have identified an approach to at least partly address the above issues. In one example approach, a method for an engine is provided comprising, pumping oil via a lower pressure pump to piston cooling jets while separately pumping oil via a higher pressure oil pump to a cylinder head. In this way, distinct pumps can be employed to supply oil at different pressures and volumes as demanded by different components of the engine.
For example, an oil delivery system in an engine may comprise at least two electric oil pumps, each drawing oil from a common, shared oil sump and returning oil back to the common, shared sump independent of each other. One pump may be a lower pressure pump communicating fluidly with a low pressure circuit which supplies oil at lower pressure to cool pistons via piston cooling jets. The other pump may be a higher pressure pump fluidly coupled to a high pressure circuit which provides oil at a higher pressure to a cylinder head, bearings, a variable valve operation system and/or a turbocharger. Thus, during engine operation, the lower pressure pump may supply oil only to piston cooling jets, and may not supply oil to the cylinder head, bearings, the variable valve operation system or a turbocharger. Simultaneously, the higher pressure pump may deliver oil only to the cylinder head, bearings, the variable valve operation system and/or the turbocharger, and may not provide oil to the piston cooling jets.
In this way, oil may be supplied separately to different groups of engine components, the components grouped based on their differing oil pressure and flow requirements, without incurring a loss in hydraulic power. By using separate pumps, each pump may be activated independently based on the lubrication and/or cooling requirements of components coupled to a given pump. Further, the pumps may be simultaneously operated at different speeds and pressures based on existing engine operating conditions and component requirements. As such, this allows each pump to be sized according to the specific output demands made on that pump, enabling a reduction in power consumption and consequently, an improvement in fuel economy. Thus, non-overlapping pressure and flow conditions may be satisfied by grouping components having higher flow and lower pressure lubrication requirements separate from lower flow and higher pressure lubrication requirements, while offering the flexibility to modify pump operation with operating conditions, such as warm-up temperature profiles.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.