Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Transmission system (clutch)
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Transmission system (clutch)
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Subject: Autopart Merchandizing
Class: Senior Secondary 2
Term: 1st Term
Week: 2
Theme: Automobile Parts
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Identify various parts of clutch. State the functions of the parts identified above.
Automobile Parts disengage the clutch.
4. Diaphragm Spring (or Coil Springs): Description: A large, conical, dish-shaped spring made of high-strength steel, located within the pressure plate assembly. Some older or heavy-duty systems use multiple coil springs.
Function: Provides the necessary clamping force on the pressure plate to hold the clutch disc against the flywheel. When the clutch pedal is depressed, the release bearing pushes on the center of the diaphragm spring, causing its outer edge to pull the pressure plate away from the clutch disc, thus disengaging the clutch.
5. Release Bearing (Throw-out Bearing): Description: A specialized bearing designed to reduce friction between the rotating diaphragm spring (or release levers) and the stationary clutch fork.
Function: When the clutch pedal is pressed, the clutch fork pushes the release bearing forward. The bearing then presses against the fingers of the diaphragm spring, causing it to deform and release the clamping force on the clutch disc.
6. Clutch Fork: Description: A pivoted lever, typically made of cast metal, with one end connected to the clutch pedal linkage (cable or hydraulic pushrod) and the other end engaging the release bearing.
Function: Acts as a lever to transfer the mechanical force from the clutch pedal (via the linkage) to the release bearing, pushing it towards the pressure plate.
7. Clutch Pedal and Linkage (Cable or Hydraulic System): Description: The pedal inside the driver's compartment is connected to the clutch fork either by a mechanical cable or a hydraulic system (master cylinder, slave cylinder, and fluid lines).
Function: Allows the driver to manually engage or disengage the clutch. Pressing the pedal activates the linkage, which moves the clutch fork and release bearing.
8. Pilot Bearing/Bushing: Description: A small bearing or bronze bushing located in the center of the flywheel (or end of the crankshaft).
Function: Supports the front end of the transmission input shaft, ensuring it remains concentric with the crankshaft. This prevents the input shaft from wobbling when the clutch is disengaged.
C. How the Clutch Works (Simplified Operation)
Clutch Engaged (Pedal Up): The diaphragm spring in the pressure plate assembly firmly presses the clutch disc against the flywheel. Friction between these surfaces transmits engine power directly to the transmission input shaft, and thus to the wheels.
Clutch Disengaged (Pedal Down): The driver presses the clutch pedal. This action, via the linkage and clutch fork, pushes the release bearing against the diaphragm spring. The diaphragm spring flexes, pulling the pressure plate away from the clutch disc. The clutch disc is now free to rotate independently of the flywheel, disconnecting engine power from the transmission. This allows for smooth gear changes or stopping the vehicle without stalling the engine.
3. Teaching and Learning Activities Teacher Activities:
1. Introduction (10 minutes): Begin by asking students about their experiences with manual transmission vehicles in Nigeria (e.g., "Danfo" buses, taxis, trucks). How do drivers change gears? What sound does a vehicle make when starting? Introduce the concept of a "clutch" as the device that makes these actions possible. State the learning objectives clearly.
2. Visual Presentation (15 minutes): Display clear diagrams of a complete clutch assembly and individual clutch components (e.g., using a projector, chart, or whiteboard).
If available and safe: Bring actual clutch components (flywheel, clutch disc, pressure plate, release bearing, clutch fork) to the classroom for physical demonstration.
3. Detailed Explanation of Parts and Functions (20 minutes): Systematically go through each major part of the clutch system (Flywheel, Clutch Disc, Pressure Plate Assembly, Diaphragm Spring, Release Bearing, Clutch Fork, Pilot Bearing). For each part, describe its appearance and precise function as detailed in the "Key Concepts" section. Use analogies to simplify complex ideas (e.g., "the clutch disc is like a brake pad, creating friction"). Explain the role of each part in the overall engagement and disengagement process.
4. Interactive Q&A and Discussion (10 minutes): Pose questions to students about the identity and function of various parts. Encourage students to ask questions and clarify any misunderstandings. Facilitate a brief discussion on scenarios where a clutch might fail Transmission system (clutch)
Term: 1st Term Week: 1 ---
1. Overview and Learning Objectives This topic introduces learners to a critical component of a vehicle's transmission system: the clutch. Understanding the clutch is fundamental for any individual aspiring to work in autoparts merchandising, vehicle maintenance, or even just as a knowledgeable vehicle owner in Nigeria. The clutch facilitates the transfer of power from the engine to the gearbox, enabling smooth vehicle movement, starting, and gear changes – operations essential for the multitude of manual transmission vehicles on Nigerian roads, from commercial buses ("Danfo") and taxis to private cars and motorcycles ("Okada"). Upon completion of this lesson, students will be able to: Name and point out the different components that make up a vehicle's clutch system. Explain the specific function of each part of the clutch and why it is important for the vehicle's operation. This knowledge is directly applicable to real-world scenarios in Nigeria, such as diagnosing common vehicle issues, advising customers on clutch part replacements in an autoparts store, and appreciating the mechanics behind daily commuting in Nigerian towns and cities.
2. Key Concepts and Explanations A. Introduction to the Clutch System The clutch is a mechanical device that connects and disconnects the engine from the transmission (gearbox). It is an essential component in vehicles with manual transmissions. Its primary purpose is to allow the driver to: Start the vehicle smoothly from a standstill. Change gears without damaging the transmission. Temporarily disconnect the engine from the driven wheels while the engine is running (e.g., at traffic lights or during gear changes). Without a functional clutch, a manual transmission vehicle cannot be operated effectively or safely. B. Main Components of a Single-Plate Dry Clutch (Most Common Type) The clutch system comprises several interconnected parts that work in harmony. The focus here is on the single-plate dry clutch, which is widely used in Nigerian vehicles due to its simplicity and effectiveness.
1. Flywheel: Description: A heavy, circular metallic disc attached to the crankshaft at the rear of the engine. It is considered part of the engine but forms the primary friction surface for the clutch.
Function: Inertia: Stores rotational energy, helping the engine run smoothly by damping crankshaft speed fluctuations.
Clutch Friction Surface: Provides a smooth, machined surface against which the clutch disc can be pressed, transmitting engine torque.
Ring Gear: Has teeth around its periphery for the starter motor to engage, turning the engine over to start.
2. Clutch Disc (Friction Plate): Description: A thin, circular plate with friction material (similar to brake pads) riveted to both sides. It has a central hub splined to the transmission input shaft, allowing it to slide along the shaft but rotate with it.
Function: Torque Transmission: When clamped between the flywheel and the pressure plate, it transmits the engine's rotational power to the transmission input shaft due to friction.
Shock Absorption: Contains springs (torsional springs) within its hub that cushion the engagement of the clutch, reducing shock to the driveline during gear changes and starts.
3. Pressure Plate Assembly (Clutch Cover Assembly): Description: A metal cover assembly typically bolted to the flywheel. It contains the pressure plate, diaphragm spring (or coil springs), and sometimes release levers.
Function: Clamping Force: Exerts a strong, consistent clamping force on the clutch disc, pressing it firmly against the flywheel. This force is crucial for effective torque transmission.
Releasing Mechanism: Houses the spring mechanism (e.g., diaphragm spring) that, when acted upon by the release bearing, lifts the pressure plate to disengage the clutch.
4. Diaphragm Spring (or Coil Springs): Description: A large, conical, dish-shaped spring made of high-strength steel, located within the pressure plate assembly. Some older or heavy-duty systems use multiple coil springs.
Function: Provides the necessary clamping force on the pressure plate to hold the clutch disc against the flywheel. When the clutch pedal is depressed, the release bearing pushes on the center of the diaphragm spring, causing its outer edge to pull the pressure plate away from the clutch disc, thus disengaging the clutch. 5. *Release Bearing Bearing). For each part, describe its appearance and precise function as detailed in the "Key Concepts" section. Use analogies to simplify complex ideas (e.g., "the clutch disc is like a brake pad, creating friction"). Explain the role of each part in the overall engagement and disengagement process.
4. Interactive Q&A and Discussion (10 minutes): Pose questions to students about the identity and function of various parts. Encourage students to ask questions and clarify any misunderstandings. Facilitate a brief discussion on scenarios where a clutch might fail (e.g., "clutch slipping," "hard pedal").
5. Summarization (5 minutes): Recap the main parts identified and their functions. Emphasize the importance of the clutch for vehicle operation and safety.
Student Activities:
1. Active Listening and Note-Taking: Students will listen attentively to explanations and take comprehensive notes on clutch parts and their functions.
2. Visual Identification: Students will identify various clutch components from diagrams, charts, or actual physical parts presented by the teacher.
3. Questioning: Students will ask clarifying questions about the components and their roles.
4. Participation in Discussions: Students will contribute to class discussions, sharing their observations and understanding.
5. Labeling Exercise: Students may be given unlabeled diagrams of a clutch assembly and tasked with labeling the parts.
4. Guided Practice (With Solutions) The teacher should use diagrams or descriptions for these questions.
Question 1: Observe the image or listen to the description of a component that is bolted to the engine's crankshaft and provides a flat surface for the clutch disc to engage. a. Identify this component. b. What is its primary role in the clutch system?
Solution 1: a. Flywheel b. The flywheel provides a friction surface for the clutch disc to engage, allowing the transfer of engine power to the transmission. It also adds inertia to smooth out engine operation and houses the ring gear for the starter motor.
Question 2: A mechanic in a workshop in Abuja observes that a vehicle's clutch disc is heavily worn, with most of the friction material gone. a. What is the name of this specific part? b. How would this severe wear affect the vehicle's ability to move, and why?
Solution 2: a. Clutch Disc (or Friction Plate) b. If the friction material on the clutch disc is severely worn, the vehicle will experience clutch slippage. This means the clutch disc cannot effectively grip the flywheel when engaged. The engine will rev high, but little power will be transmitted to the wheels, resulting in poor acceleration and inability to move the vehicle efficiently, especially uphill or with a load (e.g., a fully loaded "Danfo"). This is because there isn't enough friction to transfer the engine's torque.
Question 3: During clutch disengagement, a specific bearing is pushed by the clutch fork to act on the diaphragm spring. a. Name this bearing. b. Explain why its proper functioning is critical for smooth gear changes.
Solution 3: a. Release Bearing (or Throw-out Bearing) b. The release bearing's proper functioning is critical for smooth gear changes because it ensures that the diaphragm spring is accurately and smoothly pushed to release the clamping pressure on the clutch disc. If the release bearing is faulty (e.g., seized or worn), it might prevent full disengagement, cause grinding noises, or make the clutch pedal stiff, thereby hindering the driver's ability to change gears smoothly without resistance or damage to the gearbox.
5. Independent Practice (Questions Only)
1. List any six (6) main components of a vehicle's clutch system.
2. Draw a simple, labeled diagram illustrating the connection between the flywheel, clutch disc, and pressure plate.
3. Describe the primary function of the diaphragm spring within the clutch assembly.
4. Why is the friction material on the clutch disc essential for power transmission?
5. What would be the likely symptom if the pilot bearing were completely worn out or missing?
6. Explain the role of the clutch fork in the disengagement process.
7. If a vehicle owner in Lagos observes that his car struggles to climb an overhead bridge, and the engine speed increases disproportionately without a corresponding increase in vehicle speed, which clutch component is most