LO 10-2 Describe the purpose, properties, function, composition, types, and applications of diesel engine lubricating oils

Purpose and Function of the Lubrication System

Lubrication systems in a diesel engine are built primarily to circulate pressurized engine oil to supply moving parts with a film of lubricating oil Figure 4. Lubricating oil stored in an oil pan is picked up by an oil pump and circulated through the engine by way of oil galleries and other drilled passages. Some oil is used to cool pistons by spraying the underside of piston crowns with pressurized oil. To remove this extra heat picked up by the oil in diesel engines, the lubricating system uses an oil cooler. A variety of valves regulate oil pressure, and filters remove contaminants trapped by engine oil. The lubrication system’s design, and the construction and operation of its components, is also organized to perform the following tasks:

1. Reduce friction between moving parts to minimize engine wear and the creation of heat.
2. Cool a variety of internal engine parts and remove some heat from the engine.
3. Clean contaminants from inside the engine and remove dirt and abrasives from lubricating oil.
4. Assist in the sealing of the combustion chamber by forming a film between the piston rings and the cylinder wall. (Most seals require or perform better with a film of lubricant on rotating surfaces.)
5. Absorb shock loads between bearings and gears, thus cushioning and protecting engine parts while minimizing engine noise production.
6. Store an adequate supply of oil for lubricating internal engine parts.
7. Minimize corrosion of internal engine components.
8. Neutralize combustion contaminants.

FIGURE 10-4: A simplified diagram of a diesel engine lubrication system.

FIGURE 10-5: A screen from a Caterpillar Electronic Technician (Cat ET), where programable engine protection system monitoring conditions are adjusted.

Throughout this chapter, each of the lubrication system components will be examined to understand how they function to achieve the intended purpose of the lubrication system overall. The lubrication system in today’s engines also performs each of its functions by incorporating a variety of physical and virtual sensor technologies to protect the engine from damage. Data from many of the sensors is integrated into the operation of the engine protection system, which is one of many functions regulated by software within the engine control unit (ECU). The engine protection system alerts the driver to engine conditions that can potentially cause catastrophic engine failure. Note that the engine protection system is configured to either only alert the driver, alert and shut down, or alert and derate the engine power Figure 5. Derating the engine power has two purposes: The first is to provide an operator with the incentive to have the condition diagnosed and corrected; the other is to change the operating conditions that could result in engine failure. For example, high oil temperature could be caused by low oil volume combined with high engine load. Reducing engine power in turn lowers the amount of heat absorbed by the oil. Typically, the engine requires an ignition cycle to reset the engine protection system alert.

Virtual sensors are not actually real, like physical sensors. Instead, software makes the sensor data appear real. Virtual sensors typically collect data from other sensors to predict or calculate an unknown and difficult to measure physical quantity. An engine oil life monitor is an example of a virtual sensor. Data from the engine, such as the amount of fuel burned, engine speed, oil temperature, and so on, are plugged into an algorithm used to predict how much service life remains for the engine oil before it requires draining. On the other hand, real, physical sensors in the lubrication systems include:

• Low oil pressure warning switches
• Oil pressure sensors
• Oil level sensors to warn if inadequate oil volume is present before a low-pressure condition develops
• Oil temperature sensors
• Oil quality sensors