Oil pump (internal combustion engine)

The oil pump in an internal combustion engine circulates engine oil under pressure to the rotating bearings, the sliding pistons and the camshaft of the engine. This lubricates the bearings, allows the use of higher-capacity fluid bearings and also assists in cooling the engine.

As well as its primary purpose for lubrication, pressurized oil is increasingly used as a hydraulic fluid to power small actuators. One of the first notable uses in this way was for hydraulic tappets in camshaft and valve actuation. Increasingly common recent uses may include the tensioner for a timing belt or variators for variable valve timing systems.

The type of pump used varies. Gear pumpstrochoid pumps and vane pumps are all commonly used. Plunger pumps have been used in the past, but these are now only used rarely, for small engines.

To avoid the need for priming, the pump is always mounted low-down, either submerged or around the level of the oil in the sump. A short pick-up pipe with a simple wire-mesh strainer reaches to the bottom of the sump.

For simplicity and reliability, mechanical pumps are used, driven by mechanical geartrains from the crankshaft. Reducing pump speed is beneficial and so it is usual to drive the pump from the cam (if this is mounted in the cylinder block) or distributor shaft, which turns at half engine speed. Placing the oil pump low-down uses a near-vertical drive shaft, driven by helical skew gears from the camshaft. Some engines, such as the Fiat twin cam engine of 1964, began as OHV engines with an oil pump driven from a conventional camshaft in the cylinder block. When the twin overhead cam engine was developed, the previous oil pump arrangement was retained and the camshaft became a shortened stub shaft. Even when the distributor position was moved from the previous block-mount to being mounted on the cylinder head camshafts, the oil pump drive remained in the same position, the unused distributor position now covered by a blanking plate.Small engines, or scooters may have internal gear pumps mounted directly on their crankshaft.

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Wikipedia