Lesson Notes By Weeks and Term v3 - Senior Secondary 3
Lubrication
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Lubrication
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Subject: Auto Mechanical Works
Class: Senior Secondary 3
Term: 2nd Term
Week: 1
Theme: Engine System
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State reasons for lubrication List the components of lubrication system State the ir functions Differentiate betweenengine oil and gear oil
Pressure Regulator): Function: Located in the oil pump or filter housing, it limits the maximum oil pressure in the system. If the pump output pressure exceeds a preset limit, the valve opens, allowing excess oil to return to the sump, preventing damage to the system from excessive pressure.
6. Oil Galleries/Passages: Function: A network of drilled passages and channels within the engine block and cylinder head. These distribute the pressurized, filtered oil from the pump to all critical moving parts, such as crankshaft bearings, camshaft bearings, piston pin bushes, and valve train components.
7. Oil Pressure Switch/Sensor and Gauge/Warning Light: Function: The switch or sensor monitors oil pressure in the main gallery. If the pressure drops below a safe operating level (e.g., due to low oil level or pump failure), it activates a warning light on the dashboard to alert the driver. A gauge provides a continuous reading of oil pressure.
Context: Drivers of vehicles like tokunbo (imported used vehicles) must pay attention to this warning light.
8. Dipstick: Function: A graduated rod inserted into the oil sump, used to manually check the oil level in the engine. It has "MIN" and "MAX" marks to indicate the acceptable oil level range.
Context: A common tool used by every Nigerian driver and mechanic for routine checks.
9. Crankcase Ventilation System (e.g., PCV Valve): Function: Removes blow-by gases (unburnt fuel and combustion by-products) that escape past the piston rings into the crankcase. These gases can contaminate the oil and build up pressure. The PCV (Positive Crankcase Ventilation) valve directs these gases back into the intake manifold to be re-burnt in the engine. This prevents oil contamination and sludge formation. C. Differentiating Engine Oil and Gear Oil While both are lubricants, engine oil and gear oil are formulated differently to meet the unique demands of their respective applications.
1. Engine Oil (Motor Oil): Primary Function: Lubricates engine components, cools, cleans, seals, and protects against corrosion and wear.
Operating Environment: High temperatures (up to 200°C in some parts), presence of combustion by-products (acids, soot), significant shear forces.
Key Characteristics: Viscosity: Varies with temperature (multi-grade oils like 15W-40, 20W-50 commonly used in Nigeria for petrol/diesel engines). The "W" (winter) rating indicates cold-start flow, while the second number indicates viscosity at operating temperature.
Additives: Contains a complex blend of additives: Detergents/Dispersants: To keep engine clean and suspend contaminants.
Anti-wear agents: To protect moving parts.
Anti-oxidants: To prevent oil breakdown at high temperatures.
Viscosity Index Improvers: To maintain stable viscosity across temperature ranges. Corrosion inhibitors, anti-foam agents.
Classifications: Primarily by SAE (Society of Automotive Engineers) viscosity grade (e.g., SAE 20W-50, SAE 10W-30) and API (American Petroleum Institute) service classification (e.g., "S" for Spark Ignition engines like SN, SM, SL; "C" for Compression Ignition/Diesel engines like CK-4, CJ-4, CI-4). The higher the second letter in API 'S' category (e.g., SN is newer/better than SM), the more advanced the oil.
Examples: SAE 20W-50 API SL/CF (common in older Nigerian vehicles), SAE 15W-40 API CJ-4 (for diesel trucks).
2. Gear Oil (Transmission Oil/Axle Oil): Primary Function: Lubricates gears, bearings, and shafts in manual transmissions, differentials (rear axles), and transaxles. It must withstand extreme pressure and shock loads.
Operating Environment: High pressure at gear mesh points, sliding friction, often lower temperatures than engine oil but can get hot under heavy load. No combustion by-products.
Key Characteristics: Viscosity: Generally much higher viscosity than engine oil to provide a thicker film under extreme pressure (e.g., SAE 90, SAE 80W-90, SAE 75W-140).
Additives: Characterized by Extreme Pressure (EP) additives. These additives form a protective film on gear teeth surfaces under high load and temperature, preventing metal-to-metal contact (e.g., sulphur-phosphorus compounds). Also contains anti-wear, anti-foam, and corrosion inhibitors.
Classifications: Primarily by SAE viscosity grade (e.g., SAE 90, 80W-90) and API GL (Gear Lubricant) service classification (e.g., GL-1 to GL-6). GL-4 and GL-5 are most common, with GL-5 providing higher EP protection for hypoid gears in differentials, often found in rear-wheel-drive vehicles like pickups and buses.
Examples:** SAE 90 API GL-4 (for 75W-140).
Additives: Characterized by Extreme Pressure (EP) additives. These additives form a protective film on gear teeth surfaces under high load and temperature, preventing metal-to-metal contact (e.g., sulphur-phosphorus compounds). Also contains anti-wear, anti-foam, and corrosion inhibitors.
Classifications: Primarily by SAE viscosity grade (e.g., SAE 90, 80W-90) and API GL (Gear Lubricant) service classification (e.g., GL-1 to GL-6). GL-4 and GL-5 are most common, with GL-5 providing higher EP protection for hypoid gears in differentials, often found in rear-wheel-drive vehicles like pickups and buses.
Examples: SAE 90 API GL-4 (for manual transmissions), SAE 80W-90 API GL-5 (for differentials).
Context: Using engine oil in a gearbox designed for gear oil (or vice-versa) can lead to rapid wear and component failure due to insufficient lubrication or inappropriate additive packages. For instance, a vehicle like a Toyota Hilux or a commercial bus (Molue) will require specific GL-5 gear oil for its differential to handle heavy loads. A. Reasons for Lubrication Lubrication is the process of reducing friction between moving surfaces by introducing a lubricant, usually oil, between them. The primary reasons for lubrication in an automotive engine and other mechanical components are:
1. Reduce Friction: When two metallic surfaces rub against each other, significant friction is generated. Lubricant forms a thin film (oil film) that separates these surfaces, converting sliding friction into fluid friction, which is significantly lower. This reduces the force required for movement.
2. Minimize Wear: Friction causes material to be scraped off the moving surfaces, leading to wear and tear. The lubricant film prevents direct metal-to-metal contact, thereby protecting the surfaces from abrasion and erosion, and extending the lifespan of components like bearings, piston rings, and cylinder walls.
3. Dissipate Heat (Cooling): The combustion process in an engine, along with friction, generates considerable heat. Engine oil circulates through the engine, absorbing heat from hot components (e.g., pistons, cylinder walls) and carrying it away to cooler parts like the oil sump, where it dissipates into the environment. This helps maintain optimal operating temperatures.
4. Clean Components: As the engine operates, by-products of combustion (e.g., carbon deposits, soot), wear particles, and sludge can accumulate. Engine oil contains detergent additives that help to suspend these contaminants and carry them to the oil filter, keeping the internal engine parts clean.
5. Seal Combustion Pressure: Engine oil forms a thin seal between the piston rings and cylinder walls. This seal prevents combustion gases from escaping past the piston into the crankcase (known as "blow-by"), thereby maintaining compression and engine power.
6. Prevent Corrosion: Many engine parts are made of steel and are susceptible to rust and corrosion, especially in humid environments like many parts of Nigeria. Lubricating oil contains anti-corrosion additives that coat these metal surfaces, protecting them from moisture and acids formed during combustion.
7. Dampen Shock and Noise: The oil film also acts as a hydraulic cushion, absorbing some of the mechanical shocks and reducing vibration and noise generated by moving parts, especially in bearings and gear meshes. B. Components of a Lubrication System and Their Functions A typical automotive engine lubrication system (pressure-fed system) comprises several key components working in concert:
1. Oil Sump (Oil Pan): Function: This is the reservoir for the engine oil, located at the bottom of the engine. It collects oil that drains from the engine components and allows it to cool. It also houses the oil pickup tube.
Context: Often vulnerable to damage from rough roads or potholes common in Nigeria, leading to oil leaks.
2. Oil Pickup Tube/Strainer: Function: A tube with a mesh screen (strainer) that extends into the oil sump. It draws oil from the sump and prevents large debris (like sludge or metal particles) from entering the oil pump and the rest of the lubrication system.
3. Oil Pump: Function: The heart of the lubrication system. It draws oil from the sump through the pickup tube and circulates it under pressure throughout the engine. Common types include gear pumps and rotor pumps, driven by the engine's crankshaft or camshaft.
Context: A faulty oil pump can lead to catastrophic engine failure due to lack of lubrication.
4. Oil Filter: Function: Removes impurities (dirt, carbon, metal particles) from the oil before it reaches critical engine components. It ensures clean oil is circulated. Most modern engines use a full-flow filter, meaning all oil passes through it before entering the engine galleries.
Context: Regular oil and filter changes are crucial in dusty Nigerian conditions to prevent abrasive wear.
5. Pressure Relief Valve (Oil Pressure Regulator): Function: Located in the oil pump or filter housing, it limits the maximum oil pressure in the system. If the pump output pressure exceeds a preset limit, the valve opens, allowing excess oil to return to the sump, preventing damage to the system from excessive pressure.
6. Oil Galleries/Passages: * Function: A network of drilled passages and channels within the engine block and cylinder head. These distribute the pressurized, filtered oil from the pump to all critical moving parts, such as crankshaft bearings, camshaft bearings, piston pin bushes, and
A. Teacher Activities: Introduction (10 minutes): Begin by asking students about their experiences with vehicle maintenance or common issues like engine knocking. Display pictures or a short video clip of an engine (if available) showing moving parts and ask students what prevents them from grinding. Introduce the topic "Lubrication" and its critical role in vehicle longevity and performance in Nigeria. Presentation on Reasons for Lubrication (15 minutes): Use a whiteboard, projector, or charts to list and explain each reason for lubrication (reduce friction, minimize wear, dissipate heat, clean, seal, prevent corrosion, dampen shock). Provide simple analogies (e.g., applying oil to a squeaky door hinge for friction, sweeping a dusty floor for cleaning). Facilitate a brief discussion on the importance of each reason using local examples (e.g., why okada riders need frequent oil changes due to heat and dust). Explanation of Lubrication System Components (25 minutes): Display a large diagram of an engine lubrication system. Point to each component (oil sump, pickup tube, pump, filter, galleries, pressure sensor, dipstick, PCV valve) and clearly explain its function step-by-step. If possible, bring actual discarded components (e.g., oil filter, dipstick, a small oil pump if available) for students to handle and observe. Emphasize the flow of oil through the system. Differentiating Engine Oil and Gear Oil (20 minutes): Present two samples of engine oil and gear oil (if available, in clear containers) to visually compare their appearance and viscosity. Discuss the distinct operating conditions and requirements for engines versus gearboxes. Explain the critical differences in viscosity (SAE grades) and additive packages (API S vs. C, and API GL grades, especially EP additives).
Use practical examples: "Why you don't put gear oil in your car engine, or engine oil in a truck's differential." Activity Facilitation (10 minutes): Guide students through group discussions or practical identification tasks. Address questions and clarify misunderstandings. Monitor student participation and engagement.
B. Student Activities: Brainstorming (5 minutes): Students list moving parts in a vehicle and what they think prevents them from wearing out.
Note-taking: Students take comprehensive notes during the teacher's explanations.
Q&A and Discussion: Actively participate by asking questions and contributing to class discussions on the reasons for lubrication and the functions of components.
Component Identification (Group Work): In small groups, students will be given diagrams or actual components (if available) and asked to identify them and state their function.
Oil Comparison (Observation/Discussion): If samples are provided, students will observe and compare the physical properties (e.g., thickness, colour) of engine oil and gear oil, discussing the implications of their differences.
Summary Creation: Each student writes a brief summary of the key takeaways from the lesson.
Vehicle Maintenance and Longevity in Nigeria: Understanding lubrication is paramount for vehicle owners and mechanics in Nigeria. Regular oil changes with the correct type of oil (engine and gear oil) are crucial for extending the life of vehicles operating under challenging conditions, such as dusty roads, heavy loads, and stop-and-go traffic in cities like Lagos or Abuja. This directly translates to cost savings for individuals and businesses, reducing the frequency of expensive engine or transmission repairs. For instance, a Keke Napep operator who understands the importance of frequent oil changes will likely save more money on repairs and keep his tricycle running longer than one who neglects it.
Career Opportunities and Entrepreneurship: The knowledge gained in this topic is fundamental for aspiring automotive technicians, mechanics, and spare parts dealers. It directly prepares students for careers in vehicle servicing, oil sales, or even specialized roles in lubricant testing. A skilled mechanic who can diagnose lubrication issues and recommend appropriate solutions (e.g., explaining why a particular viscosity of oil is needed for an aging vehicle vs. a new one) is highly valued in local garages and workshops across Nigeria.
Environmental and Safety Implications: Proper disposal of used engine and gear oil is a significant environmental concern in Nigeria. This lesson highlights the need for responsible oil changes and disposal methods to prevent soil and water pollution. From a safety perspective, understanding lubrication failure (e.g., a sudden drop in oil pressure) can prompt a driver to take immediate action, preventing engine seizure and potential road accidents, a common cause of breakdowns on Nigerian highways. Educating the public on oil check procedures can improve road safety.