Lesson Notes By Weeks and Term v4 - SHS 2

Lesson Video

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Performance objectives

• Describe the three main types of lubrication systems.
• Identify and explain the functions of different oil pumps.
• Describe the various types of oil filters and their roles.
• Compare the advantages and disadvantages of each system.

Lesson summary

This lesson introduces the "lifeblood" of an engine: the lubrication system. Just as the human body needs blood to circulate, reduce friction in our joints, and carry away waste, an engine needs oil to perform similar functions. In Ghana, we see engines everywhere – in trotros, taxis, private cars, Okada motorbikes, generators, and even fishing boats. Understanding how they stay lubricated is fundamental to understanding how they work, how to maintain them, and how to prevent costly damage. This knowledge is essential for any student aspiring to be an engineer, a skilled mechanic, or even a responsible vehicle owner.

Lesson notes

A. Why is Lubrication Necessary? The Functions of Engine Oil

Before we discuss the systems, we must understand *why* we need to lubricate an engine. Engine oil has five critical jobs: Lubricate: The main job is to create a thin film of oil between moving metal parts (like pistons and cylinders, or the crankshaft and its bearings). This reduces friction, preventing wear and tear. *Analogy:* Think of rubbing your dry hands together very fast. They get hot and it feels rough. Now, imagine putting some lotion or oil on them first. They slide easily with much less heat. That's what oil does for engine parts. Cool: As the oil circulates, it absorbs heat from hot areas like the bottom of the pistons and carries it away to the oil pan (sump) where it can cool down. It acts as a secondary cooling system after the main radiator. Clean: Oil contains detergents that clean the inside of the engine. It picks up tiny metal particles, carbon from combustion, and other dirt, and carries them to the oil filter. Seal: The oil film helps to seal the gap between the piston rings and the cylinder wall. This prevents combustion gases from leaking past the piston (blow-by) and maintains good engine compression and power. Prevent Rust & Corrosion: The oil coats all internal parts, protecting them from oxygen and moisture which would otherwise cause rust. B. Types of Lubrication Systems

There are three main systems used to deliver oil to the parts that need it. Mist Lubrication System (or Petroil System) How it Works: This is the simplest system. The lubricating oil is mixed directly with the petrol (fuel) before it enters the engine. As the fuel-air mixture moves through the engine's crankcase, the fuel evaporates, leaving behind a fine mist of oil droplets that coat and lubricate the moving parts. Where it's Used: Primarily in small, simple two-stroke engines. Ghanaian Examples: Chainsaws used for cutting wood, many "Okada" or "Aboboyaa" motorbikes, outboard motors on fishing canoes, leaf blowers, and some small portable generators. Advantages: Very simple and cheap to build (no pump, filter, or sump). Lightweight. Disadvantages: Less effective lubrication compared to other systems. The oil is burned along with the fuel, creating visible blue smoke and causing air pollution. Requires the user to correctly mix the oil and petrol in the right ratio. Incorrect mixing leads to rapid engine damage. Wet Sump Lubrication System How it Works: This is the most common system in passenger cars and commercial vehicles. The engine's oil supply is stored in a pan, called the oil sump or oil pan, located at the very bottom of the engine. An oil pump, submerged in the oil, draws the oil up through a pickup tube and screen. It then forces the pressurised oil through an oil filter to clean it, and then through internal passages (called oil galleries) to all the critical moving parts. Gravity then causes the oil to drip back down into the sump, and the cycle repeats. Oil's Journey in a Wet Sump System: Oil sits in the sump. Oil pump draws oil through a pickup screen. Pump pressurises the oil and sends it to the oil filter. Clean oil flows through oil galleries to the crankshaft, connecting rods, camshaft, and cylinder walls. Oil drains back down into the sump by gravity. Where it's Used: The vast majority of vehicles on Ghanaian roads. Ghanaian Examples: Toyota Corolla, Hyundai Accent, Ford Ranger, Kantanka cars, trotro buses (like a VW Transporter or Toyota Hiace), and most stationary generators. Advantages: Reliable and effective lubrication. Relatively simple and cost-effective design. All components are contained within the engine block. Disadvantages: Under extreme cornering, braking, or acceleration (like in racing), the oil can slosh away from the pump's pickup tube, causing a temporary loss of oil pressure (oil starvation), which can destroy the engine. The engine must sit higher to accommodate the deep oil pan at the bottom. Dry Sump Lubrication System How it Works: This is a high-performance system. The oil is not stored at the bottom of the engine. Instead, it is stored in a separate, external oil tank or reservoir. This system uses two oil pumps: Scavenge Pump: A high-capacity pump that sucks (scavenges) all the oil out of the shallow pan at the bottom of the engine and sends it to the external tank. Pressure Pump: This pump draws clean, cool oil from the external tank, pressurises it, and sends it through the filter and into the engine's oil galleries, just like in a wet sump system. Where it's Used: High-performance racing cars, some supercars, and heavy-duty industrial or agricultural machinery. It is not common in everyday road cars. Examples: Formula 1 cars, Rally cars, some Porsche and Ferrari models. Advantages: Prevents oil starvation: Because oil is constantly supplied from the external tank, the engine never loses oil pressure, no matter how hard the vehicle is cornering or braking. Increased oil capacity: The external tank can hold more oil, which helps with cooling. Lower engine mounting: The oil pan is very shallow, so the entire engine can be mounted lower in the vehicle. This lowers the centre of gravity and improves handling. Disadvantages: Much more complex, with extra pumps, hoses, and an external tank. More expensive and heavier than a wet sump system.

C. Oil Pumps and Oil Filters Oil Pumps

Evaluation guide

• Describe types of lubrication systems, oil pumps and oil filters
• G
• roup work/collaborative learning:
• In a fair mixed group learners use appropriate sketches or chart to describe types of