C9 On-Highway Engines Lubrication System Caterpillar

Illustration 1	g01112073
(1) Unit injector hydraulic pump (2) High pressure relief valve (3) Oil passage to the rocker arms (4) High pressure oil line (5) Valve mechanism cover (6) High pressure oil passage (7) Oil supply line to the unit injector hydraulic pump (8) Cylinder head gallery (9) Oil gallery plug (10) Piston cooling jets (11) Camshaft bearings (12) Oil filter bypass valve (13) Oil cooler bypass valve (14) Main oil gallery (15) Passage to front housing (16) Turbocharger oil supply line (17) Passage to camshaft idler gear bearing (18) Passage to cylinder block (19) Passage to oil pump idler gear bearing (20) Engine oil filter (21) Engine oil cooler (22) Main bearings (23) Engine oil pump (24) Oil pump bypass valve (25) Passage to engine oil pan (26) Engine oil pan

The engine oil pump (23) is mounted to the bottom of the cylinder block. The oil pump is located inside the oil pan (26). The engine oil pump (23) pulls oil from the engine oil pan (26). The engine oil pump pushes the oil through the passage to the engine oil cooler (21). Oil then flows through engine oil filter (20). The filtered oil then enters the turbocharger oil supply line (16). The filtered oil also enters the main oil gallery (14).

Illustration 2	g01112096
(13) Oil cooler bypass valve (20) Oil filter (12) Oil filter bypass valve (21) Oil cooler

Illustration 3	g01112098
(1) Unit injector hydraulic pump

The main oil gallery (14) distributes oil to the following areas: main bearings (22) , piston cooling jets (10) and camshaft bearing (11). Oil from main oil gallery (14) exits the front of the block. The oil then enters a groove that is cast in the front housing.

Oil enters the crankshaft through holes in the bearing surfaces (journals) for the main bearing (22). Passages connect the bearing surface (journal) for the main bearing (22) with the bearing surface (journal) for the connecting rod.

The front housing passage sends the oil flow in two directions. At the upper end of the passage, oil is directed back into the block. The oil then flows up to the cylinder head gallery (8) through passage (3) to the rocker arm mechanism. A passage (19) sends oil to the oil pump idler gear bearing.

Oil from the front main bearing enters a passage (17) to the camshaft idler gear bearing. Oil passages in the crankshaft send oil from all the main bearings (22) through the connecting rods to the connecting rod bearings.

Note: Engines that are equipped with an auxiliary oil filter will receive oil from a port. The filtered oil will be returned to the engine oil pan (26).

The unit injector hydraulic pump (1) is a gear-driven axial piston pump. The unit injector hydraulic pump raises the engine oil pressure from the typical operating oil pressure to the actuation pressure that is required by the unit injectors.

The oil circuit consists of a low pressure circuit and a high pressure circuit. The low pressure circuit typically operates at a pressure of 240 kPa (35 psi) to 480 kPa (70 psi). The low pressure circuit provides engine oil that has been filtered to the unit injector hydraulic pump (1). Also, the low pressure circuit provides engine oil that has been filtered to the lubricating system of the engine. Oil is drawn from the engine oil pan (26). Oil is supplied through the engine oil cooler (21) and engine oil filter (20) to both the engine and the unit injector hydraulic pump (1).

The high pressure circuit provides actuation oil to the unit injector. The high pressure circuit operates in a pressure range typically between 6 MPa (870 psi) and 25 MPa (3626 psi). This high pressure oil flows through a line into the cylinder head. The cylinder head stores the oil at actuation pressure. The oil is ready to actuate the unit injector. Oil is discharged from the unit injector under the valve cover so that no return lines are required.

After the lubrication oil's work is done, the lubrication oil returns to the engine oil pan.

The oil pump bypass valve (24) limits the pressure of the oil that is coming from the engine oil pump (23). The engine oil pump (23) can pump more than enough oil into the system. When there is more than enough oil, the oil pressure increases. When the oil pressure increases, the oil pump bypass valve (24) will open. This allows the oil that is not needed to go back to the suction side of the engine oil pump (23).

The bypass valves (12) and (13) will open when the engine is cold (starting conditions). Opening the bypass valves achieves immediate lubrication of all components. Immediate lubrication is critical. Cold oil with high viscosity causes a restriction to the oil flow through engine oil cooler (21) and engine oil filter (20). The engine oil pump (23) sends the cold oil through the oil cooler bypass valve. This causes the oil to bypass the engine oil cooler (21). The oil filter bypass also allows the oil to bypass the engine oil filter (20). The oil is then pumped through the turbocharger oil supply line (16) and the main oil gallery (14) in the cylinder block.

When the oil gets warm, the pressure difference in the bypass valves decreases and the bypass valves close. After the bypass valves close, there is a normal flow of oil through the engine oil cooler and the engine oil filter.

The bypass valves will also open when there is a restriction in the engine oil cooler (21) or in the engine oil filter (20). This design allows the engine to be lubricated even though engine oil cooler (21) or engine oil filter (20) are restricted.

High pressure relief valve (24) regulates high pressure in the system. When the oil pressure is at 695 kPa (100 psi) or more, high pressure relief valve (24) opens. When the high pressure relief valve opens, oil is returned to engine oil pan (26).

The oil flow continues to the engine oil cooler (21). Coolant flows through engine oil cooler (21) in order to cool the oil.

If the oil pressure differential across the engine oil cooler reaches 155 ± 17 kPa (22 ± 2 psi), the valve will open. Opening the valve allows the oil flow to bypass the engine oil cooler (21).

Approximately five percent of the oil flow is directed through an orificed passage to oil filter bypass valve (12). The oil then flows to the auxiliary oil filter (if equipped) and to the engine oil pan (26). The main oil flow now reaches the main engine oil filter (20). When the oil pressure differential across the oil filter bypass valve (13) reaches 170 kPa (25 psi), the valve opens in order to allow the oil flow to go around the oil filter (20). The oil flow continues in order to lubricate the engine components. When the oil is cold, an oil pressure difference in the bypass valve also causes the valve to open. This bypass valve then provides immediate lubrication to all the engine components when cold oil with high viscosity causes a restriction to the oil flow through the engine oil filter (20). The bypass valve will also open when there is a restriction in the engine oil filter (20). This design allows the engine to be lubricated even though engine oil filter (20) is restricted.

Note: Refer to Specifications, "Engine Oil Filter Base".

Filtered oil flows through the main oil gallery (14) in the cylinder block. Oil is supplied from the main oil gallery (14) to the following components:

• Piston cooling jets (10)

• Valve mechanism

• Camshaft bearing (11)

• Crankshaft main bearings

• Turbocharger cartridge

An oil cooling chamber is formed by the lip that is forged at the top of the skirt of the piston and the cavity that is behind the ring grooves in the crown. Oil flow for the piston cooling jet enters the cooling chamber through a drilled passage in the skirt. Oil flow from the piston cooling jet returns to the engine oil pan (26) through the clearance gap between the crown and the skirt. Four holes that are drilled from the piston oil ring groove to the interior of the piston drain excess oil from the oil ring.

Illustration 4	g01112104
(27) Breather (28) Hose

Breather (27) allows engine blowby to escape from the crankcase. The engine blowby is discharged through hose (28) into the atmosphere. This prevents pressure from building up that could cause seals or gaskets to leak.