Piston Engines - Lubrication — Page 45, Lesson 57

I want to walk you through the function of the lubrication system in a piston engine. This is the very start of the chapter, so we're building the foundation from zero. First, let's set the scene. The components inside a piston engine are subjected to three harsh things: high loads, high temperatures, and high speeds. The parts are generally made of metal, and as the moving parts slide against each other, there's a resistance to their movement. That resistance has a precise name: Friction. Now, friction doesn't stay constant. It increases as the load, temperature, and speed increase. And here's the dangerous part — the movement of the components also produces Wear, which is the loss or destruction of the metal components. So friction is the force resisting motion, and wear is the actual physical damage to the metal. The whole trick of lubrication is to reduce both friction and wear by preventing the moving surfaces from coming into contact with each other. How? By separating them with a material that has lower frictional properties than the component parts themselves. That separating substance is called a Lubricant. Now, a lubricant can come in many forms — greases, powders, and some solid materials. But this chapter concentrates specifically on Oils. And there are two ways oil can be delivered to the moving parts. The oil can be forced between the moving parts under pressure — that's called Pressure Lubrication. Alternatively, the components can be lubricated by being splashed with oil — that's Splash Lubrication. So what's the primary task of the whole lubrication system? It's to reduce friction and component wear. That's the main job. But the system also has a number of secondary functions, and the most important of those is Cooling. The flow of oil through the engine helps dissipate heat away from the internal components. As the oil flows through the engine, it also carries away the by-products of the combustion process — so it cleans the engine. The internal metal components are protected against Corrosion by the oil. And the oil also acts as a Hydraulic Medium, which reduces the shock loads between the crankshaft and the bearing, and so reduces vibration. Finally, the oil can provide the power source for the operation of a hydraulic... and that's where the excerpt cuts off, but you get the idea — the oil is doing far more than just reducing friction. Let me pull that together for you. The lubrication system has one primary job — reduce friction and wear — and then a stack of secondary jobs: cooling, cleaning, corrosion protection, acting as a hydraulic medium to cushion shock loads and reduce vibration, and potentially powering hydraulic operations. Every one of those roles comes from the same simple principle: keep the metal surfaces separated by a film of oil.