Lesson Notes By Weeks and Term v3 - Senior Secondary 1
STARTING SYSTEM
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STARTING SYSTEM
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Subject: Auto Mechanical Works
Class: Senior Secondary 1
Term: 2nd Term
Week: 6
Theme: Transmission & Braking System
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Identify the maincomponents of the starting system. State the functions of each component.
The starting system is an essential subsystem in an automobile responsible for converting the electrical energy from the battery into mechanical energy to crank the engine, initiating the combustion process. Without a functioning starting system, the engine cannot be started. 2.
1. Purpose of the Starting System: The primary purpose is to crank the engine (turn it over) at a sufficient speed (typically 100-200 RPM) to draw in the air-fuel mixture, compress it, and allow the ignition system to ignite it, thereby starting the engine's internal combustion cycle. 2.
2. Main Components of the Starting System and Their Functions: The starting system typically comprises several key components working in sequence:
1. Battery: Description: A rechargeable electrochemical cell (usually 12-volt in most Nigerian passenger vehicles) that stores electrical energy.
Function: Provides the necessary electrical current (a very high amperage, sometimes hundreds of amperes) to power the starter motor. It acts as the primary power source for the entire starting system.
2. Ignition Switch: Description: A multi-position electrical switch operated by a key, usually located on the steering column or dashboard.
Function: Controls the flow of electrical current to various vehicle systems, including the starting system. It typically has positions like "LOCK," "ACC" (Accessory), "ON" (Ignition), and "START." When turned to the "START" position, it sends a low-current signal to the starter solenoid, initiating the cranking process.
3. Starter Motor: Description: An electric motor (DC motor) designed to produce a large amount of torque for a short duration. It consists of an armature, field windings, brushes, and a commutator, all housed within a casing.
Function: Converts electrical energy from the battery into mechanical rotational energy. This rotational energy is then used to turn the engine's flywheel, thereby cranking the engine. It is designed for intermittent use due to the high current draw and heat generation.
4. Starter Solenoid (or Starter Relay): Description: An electromagnetic switch often mounted directly on the starter motor or sometimes separately on the fender well.
It contains two windings: a pull-in winding and a hold-in winding, and a plunger.
Function: Serves two main purposes: High-Current Relay: It acts as a heavy-duty relay, allowing a small current from the ignition switch to switch on a much larger current flow directly from the battery to the starter motor. This prevents high current from flowing through the ignition switch.
Pinion Engagement: It mechanically pushes the starter drive pinion gear forward to engage with the engine's flywheel ring gear before the starter motor begins to spin at full speed.
5. Starter Drive (Bendix Drive or Overrunning Clutch): Description: A mechanism, usually part of the starter motor assembly, which includes a small pinion gear.
Function: Allows the starter pinion gear to engage with the flywheel's ring gear when the starter motor is activated and then disengage once the engine starts and reaches a speed higher than the starter motor. The overrunning clutch prevents the high-speed engine from driving the slower-speed starter motor, which would damage it.
6. Flywheel / Ring Gear: Description: The flywheel is a heavy metal disc attached to the rear of the crankshaft. A toothed metal ring, called the ring gear, is pressed onto the outer circumference of the flywheel.
Function: The flywheel stores rotational energy, smoothing out engine power pulses. The ring gear provides the teeth that the starter drive's pinion gear engages with to crank the engine.
7. Battery Cables and Electrical Wiring: Description: Thick copper cables (positive and negative) connect the battery to the starter solenoid and chassis ground. Smaller gauge wires connect the ignition switch to the solenoid.
Function: Thick Cables: Carry the very high current from the battery to the starter motor with minimal voltage drop.
Smaller Wires: Carry the low-current control signal from the ignition switch to activate the solenoid.
8. Neutral Safety Switch (Automatic Transmissions) / Clutch Pedal Switch (Manual Transmissions): Description: Electrical switches integrated into the transmission or clutch linkage.
Function: A safety device that prevents the engine from starting unless the transmission is in "Park" or "Neutral" (for automatics) or the clutch pedal is fully ignition switch to the solenoid.
Function: Thick Cables: Carry the very high current from the battery to the starter motor with minimal voltage drop.
Smaller Wires: Carry the low-current control signal from the ignition switch to activate the solenoid.
8. Neutral Safety Switch (Automatic Transmissions) / Clutch Pedal Switch (Manual Transmissions): Description: Electrical switches integrated into the transmission or clutch linkage.
Function: A safety device that prevents the engine from starting unless the transmission is in "Park" or "Neutral" (for automatics) or the clutch pedal is fully depressed (for manuals). This prevents accidental vehicle movement during starting. 2.
3. Operational Sequence (How the Starting System Works):
1. The driver turns the ignition key to the "START" position.
2. The ignition switch sends a low-current electrical signal to the starter solenoid.
3. The solenoid's windings are energized, creating an electromagnetic field.
4. This field pulls a plunger, which has two effects: It closes a set of heavy-duty contacts, completing the high-current circuit directly from the battery to the starter motor. * It simultaneously pushes the starter drive's pinion gear forward to mesh with the teeth on the engine's flywheel ring gear.
5. With power supplied, the starter motor begins to spin, turning the flywheel and cranking the engine.
6. Once the engine starts and the driver releases the ignition key, the ignition switch returns to the "ON" position.
7. The solenoid de-energizes, the contacts open (cutting power to the starter motor), and a return spring pulls the pinion gear out of mesh with the flywheel. The overrunning clutch also ensures disengagement even if the key is held too long.
Example (Contextual for Nigeria): Imagine a "Danfo" (commercial bus) in Lagos not starting. A common initial check by the driver or a roadside mechanic (mechanic 'Oga') often involves checking the battery terminals for corrosion or looseness, or hitting the starter motor with a spanner. This highlights the practical importance of the battery and starter motor in common vehicle issues. If the battery is dead, the starting system lacks power. If the starter motor is faulty, it cannot convert electrical energy to mechanical energy to crank the engine.
Teacher Activities: Introduction (10 minutes): Initiate a discussion by asking students what happens when they turn a car key or press a start button. What sounds do they hear? What is the purpose of this action? Present a large diagram of a complete starting system or a physical starter motor (if available). Briefly state the lesson's objectives. Component Identification and Explanation (25 minutes): Using visual aids (charts, diagrams, projector, actual components if accessible), systematically introduce each component of the starting system. For each component (Battery, Ignition Switch, Starter Motor, Solenoid, Starter Drive, Flywheel/Ring Gear, Cables, Safety Switches): Display the component. State its name clearly. Explain its function in simple, clear terms, possibly drawing analogies. Emphasize its role in the overall starting sequence.
System Operation Sequence (15 minutes): Walk students through the step-by-step operation of the starting system from the driver turning the key to the engine cranking and the starter disengaging. Use arrows on a diagram to illustrate the flow of power and mechanical action. Encourage questions for clarification.
Practical Connection (5 minutes): Discuss common starting problems (e.g., "dead battery," "clicking sound but no crank," "starter grinding") and link them back to the components and their functions. This connects theory to practical troubleshooting, relevant for Nigerian automotive contexts.
Recap and Q&A (5 minutes): Summarize the main components and their functions. Address any remaining student questions.
Student Activities: Discussion and Brainstorming (10 minutes): Students participate in the initial discussion about vehicle starting, sharing their observations and prior knowledge.
Observation and Note-taking (25 minutes): Students carefully observe the presented diagrams/components and take detailed notes on the name and function of each starting system component. They may draw simple sketches of components. Active Listening and Questioning (15 minutes): Students listen attentively to the explanation of the system's operational sequence. They ask clarifying questions when they do not understand a concept or a component's role. Component Identification Exercise (5 minutes): If using a large diagram, the teacher points to a component, and students identify it by name. Students volunteer to state the function of specific components.
Instructions: Teachers should pose these questions to students and guide them through formulating the answers, providing the solutions after students have attempted them.
Question 1: List three essential components required for a vehicle's engine to be cranked by the starting system.
Solution: Battery: Provides the electrical power.
Ignition Switch: Initiates the starting sequence.
Starter Motor: Converts electrical energy to mechanical energy to turn the engine. (Other valid answers include Starter Solenoid, Starter Drive, Flywheel/Ring Gear.)
Commentary: This question assesses the basic identification of core components, emphasizing those absolutely necessary for the fundamental cranking action.
Question 2: Explain the primary function of the starter solenoid in the starting system.
Solution: The starter solenoid serves two main functions: As a high-current relay: It allows a small current from the ignition switch to activate a much larger current flow from the battery directly to the starter motor. This protects the ignition switch from carrying the high current needed by the starter motor.
To engage the starter drive: It mechanically pushes the starter drive's pinion gear forward to mesh with the flywheel ring gear before the starter motor spins.
Commentary: This question tests the understanding of a critical dual role of the solenoid, which is often misunderstood as just a 'switch'. It's important to differentiate its electrical and mechanical roles.
Question 3: A driver attempts to start his car in Abuja, but the engine only makes a rapid clicking sound, and the starter motor does not turn. Which component is most likely the cause of this specific symptom, and why?
Solution: The most likely cause is a discharged or weak battery.
Reason: A weak battery can supply enough voltage for the solenoid to click (energize), but it does not have enough current (amperage) to actually turn the heavy starter motor and crank the engine. The rapid clicking occurs because the solenoid tries to engage but immediately drops out due to insufficient current to maintain the pull-in winding, resulting in repeated engagement and disengagement.
Commentary: This question integrates knowledge of component function with a common real-world diagnostic scenario in Nigeria, encouraging critical thinking beyond mere memorization.
Vehicle Maintenance and Repair (Entrepreneurship): Knowledge of the starting system is a fundamental skill for aspiring auto mechanics and electricians in Nigeria. Understanding how each component works helps in diagnosing common issues like "the car won't start." This knowledge directly translates into practical skills for a lucrative career in auto repair shops across the country, from small roadside stands to large service centers. Students can explore setting up their own mobile repair services. Personal Vehicle Troubleshooting and Cost Savings: For vehicle owners in Nigeria, understanding the starting system allows for basic troubleshooting. Instead of immediately towing a vehicle to a mechanic for every starting issue, an informed individual might check for loose battery terminals, a faulty battery, or even a clicking starter solenoid, potentially saving diagnostic fees and towing costs. This empowers individuals with practical knowledge relevant to their daily lives and personal finance.
Road Safety and Reliability: A well-understood and maintained starting system contributes to vehicle reliability. Knowing the signs of an impending starter failure (e.g., slow cranking, grinding noises) can prompt timely repairs, preventing breakdowns in inconvenient or dangerous locations, especially on long journeys between Nigerian cities. This promotes safety and ensures smoother transportation within the community.