LO 10-5 Identify and describe the types, functions, construction features, and applications of diesel engine lubrication system components

Oil Pump

The oil pump is used to pressurize the lubrication system of a diesel engine. It is a positive displacement pump, usually constructed with a closed-gear or gerotor design. A gerotor pump is constructed of an inner rotor and an outer rotor. The inner rotor turns inside the outer rotor ring, which also turns. The inner rotor has one less lobe than the outer ring and is positioned off-center from the outer ring. As the lobes slide up and over one another, oil is drawn through a fixed passageway connected to the oil pump pickup tube. Oil is squeezed out into the main oil gallery through the outlet passageway behind the rotors Figure 29. The external gear pump is another common configuration for an engine oil pump. This pump has two opposing gears. A drive shaft turns one gear, which in turn rotates the opposite gear. Oil is trapped and carried around the pump between the gear teeth. A seal is formed between the gear teeth and the oil pump housing Figure 30.

FIGURE 10-29: A gerotor oil pump.

FIGURE 10-30: An internal gear oil pump.

FIGURE 10-31: Oil is drawn into the pickup tube through a screen. The pickup tube is located in the sump of the oil pan.

The lube oil is supplied under pressure to moving parts through drilled passageways in the engine called oil galleries . Most moving parts are supplied pressurized oil for lubrication; however, cylinder walls are lubricated by oil thrown off engine bearings and from oil cooler nozzles. Oil is drawn into the pump through a pickup tube and screen located in the oil pan sump Figure 31. When replacing oil pumps, they should be primed to shorten the time required to develop engine oil pressure. The pickup tube inlet screen should be cleaned and inspected for blockages.

Variable Displacement Oil Pumps
The oil pump is a common target for achieving energy reductions in today’s diesels. Several engines now use flow rate-controlled oil pumps or two-stage pumps that operate at either a high-pressure or a low-pressure setting, depending on operating requirements Figure 32. Data from the oil pressure sensor and the engine ECU calculations are used to electrically switch the oil pump between the two pressure stages, depending on engine load, speed, and oil temperature. Power consumption by the oil pump is reduced when driving in low-speed urban or off-road conditions when high oil pump volume and pressure are not required. A common type of a flow rate-controlled vane pump regulates pump delivery volume by rotating an eccentric adjustable ring that surrounds the pump vanes. The space between the pump vanes is increased or decreased to change pump output volume. A hydraulic control valve rotates the ring against spring pressure to vary the space swept by the pump vanes Figure 33.

FIGURE 10-32: The oil pressure produced from a two-stage pump with an electronically controlled pressure-relief valve.

FIGURE 10-33: A flow rate-controlled pump. Components of a variable displacement oil pump that are used to save energy. The area of the delivery space above the pump vanes is mechanically varied to optimally match engine requirements for oil pressure.