Lesson Notes By Weeks and Term v3 - Senior Secondary 1
IGNITION SYSTEM
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IGNITION 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 3 types of ignition systems. identify the maincomponents of the ignition system and statetheir functions Differentiate betweentypes of ignition systemused in motor vehicles.
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2. Ignition Switch: Function: An electrical switch operated by the driver using a key. It controls the flow of current from the battery to the ignition system (and other circuits like starting). It has "OFF," "ACC" (Accessory), "ON" (Ignition), and "START" positions.
3. Ballast Resistor (Primarily in Conventional Systems): Function: Limits the current flowing through the ignition coil's primary winding during engine operation to prevent overheating and premature coil failure. It is bypassed during starting to provide a higher voltage for easier starting.
4. Ignition Coil: Function: A step-up transformer that converts the low voltage (12V) from the battery into a very high voltage (15,000V to 40,000V or more) necessary to create a spark at the spark plugs. It consists of a primary winding (fewer turns of thick wire) and a secondary winding (many turns of thin wire) around a soft iron core.
5. Distributor (Primarily in Conventional and TCI Systems): Function: Distributes the high voltage from the ignition coil to the correct spark plug at the precise firing order and timing.
It houses: Cam: A multi-lobed component driven by the engine, which opens and closes the contact breaker points. Contact Breaker Points (Breaker Points / Points): A mechanical switch that opens and closes to interrupt the primary current flow in the ignition coil. When they open, the magnetic field collapses, inducing high voltage in the secondary winding.
Condenser (Capacitor): Connected in parallel with the contact breaker points. It absorbs the surge of current that occurs when the points open, preventing arcing across the points and ensuring a rapid collapse of the magnetic field, thus enhancing the high voltage spark.
Rotor: A rotating arm inside the distributor cap that connects the centre terminal (receiving high tension from the coil) to the appropriate spark plug terminal on the distributor cap.
Distributor Cap: A non-conductive cap that sits on top of the distributor, containing terminals for the high tension leads (spark plug wires) and a central terminal for the ignition coil. It guides the high voltage from the rotor to the correct spark plug.
6. High Tension (HT)
Leads / Spark Plug Wires: Function: Heavily insulated cables that safely carry the very high voltage from the ignition coil (via the distributor cap in older systems, or directly from coil packs in modern systems) to the spark plugs without leakage.
7. Spark Plugs: Function: Devices threaded into the engine cylinder head. They provide a gap across which the high-voltage electricity jumps, creating a spark that ignites the compressed air-fuel mixture.
8. Crankshaft Position Sensor (CPS) (In Electronic Systems): Function: Monitors the rotational speed and position of the crankshaft. This information is critical for the ECU to determine engine speed and piston position for precise ignition timing.
9. Camshaft Position Sensor (CMP) (In Electronic Systems): Function: Monitors the rotational position of the camshaft, helping the ECU identify which cylinder is on its compression stroke, which is essential for sequential fuel injection and ignition timing.
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0. Electronic Control Unit (ECU) / Engine Control Module (ECM) (In Electronic Systems): Function: The "brain" of the electronic ignition system (and engine management). It receives input from various sensors (CPS, CMP, throttle position, etc.), processes this data, and then precisely controls the ignition timing and firing sequence of the ignition coils.
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1. Ignition Coil Packs (In Electronic Systems): * Function: Instead of one central coil, modern systems use multiple individual coils (one per cylinder or one per pair of cylinders). These coil packs are directly controlled by the ECU and generate high voltage closer to the spark plugs, reducing energy loss and improving reliability. 2.5 Differentiation between Types of Ignition Systems | Feature/System | Conventional Coil Ignition | Transistorised Coil Ignition (TCI) | Electronic Ignition System (EIS) / Distributor-less Ignition (DIS) | | :----------------------- | :--------------------------------------------------------- | :--------------------------------------------------------------- | :----------------------------------------------------------------- | | Primary Current Control | Mechanical contact breaker points | Transistor (triggered by points or a sensor) | Electronic Control Unit (ECU) via sensors | | Distributor | Present (essential for high voltage distribution) | Present (essential for high voltage distribution) | Absent (replaced by 2.1 Introduction to the Ignition System The ignition system is an electrical system in an internal combustion engine responsible for generating a high-voltage spark at precisely the right moment to ignite the compressed air-fuel mixture within the engine's cylinders. This ignition initiates the power stroke, driving the engine. Without a functional ignition system, the engine cannot start or run. 2.2 Principles of Ignition The basic principle involves stepping up a low voltage (typically 12V from the battery) to a very high voltage (15,000V to 40,000V or more). This high voltage creates a spark that jumps across the gap of the spark plug electrodes, igniting the fuel mixture. The timing of this spark is crucial and must be precisely synchronized with the engine's piston position (compression stroke). 2.3 Types of Ignition Systems Ignition systems have evolved significantly over time to improve reliability, efficiency, and reduce maintenance.
The three main types are:
1. Conventional Coil Ignition System (Battery and Coil Ignition / Contact Breaker Ignition): This is the oldest type, relying on mechanical components for timing.
How it works: A 12V battery supplies current to the ignition coil's primary winding. The current flows through the ignition switch, a ballast resistor (if present), the primary winding, and then to the contact breaker points in the distributor. When the contact breaker points are closed, current builds a magnetic field in the coil. As the distributor's cam rotates, it opens the points, rapidly collapsing the magnetic field. This collapse induces a very high voltage in the secondary winding of the coil. This high voltage is then directed by the distributor rotor to the correct spark plug via the distributor cap and HT leads, causing a spark.
Characteristics: Mechanical points wear out, requiring regular maintenance (gapping, replacement). Uses a distributor to route the spark.
2. Transistorised Coil Ignition System (TCI): An improvement over the conventional system, using a transistor to handle the primary current, reducing wear on the contact breaker points.
How it works: Similar to the conventional system, but the contact breaker points (or a magnetic/Hall effect sensor) only switch a small current to activate a power transistor. This transistor then rapidly switches the high primary current of the ignition coil. This reduces arcing and wear on the points (if still present) or eliminates them entirely when using a sensor.
Characteristics: More reliable than conventional systems, reduced maintenance compared to conventional due to less wear on points (or their elimination), still uses a distributor.
3. Electronic Ignition System (EIS) / Distributor-less Ignition System (DIS): Modern systems that completely eliminate the distributor and mechanical contact points. They rely on electronic sensors and a computer (Engine Control Unit - ECU) for precise timing.
How it works: Sensors (e.g., crankshaft position sensor, camshaft position sensor) provide precise engine speed and piston position information to the ECU. The ECU then calculates the optimal spark timing and directly triggers individual ignition coils (or coil packs) for each cylinder. The high voltage is generated by these coil packs and delivered directly to the spark plugs via short HT leads or directly mounted on the spark plugs (Coil-on-Plug or COP systems).
Characteristics: Highly reliable, virtually maintenance-free, precise timing, better fuel economy, lower emissions, no distributor, uses ECU for control. 2.4 Main Components of the Ignition System and Their Functions Here are the common components, noting that some are specific to certain types of systems:
1. Battery (12V): Function: Provides the initial low voltage electrical energy required to operate the ignition system and other vehicle electrical components. It acts as the primary power source.
2. Ignition Switch: Function: An electrical switch operated by the driver using a key. It controls the flow of current from the battery to the ignition system (and other circuits like starting). It has "OFF," "ACC" (Accessory), "ON" (Ignition), and "START" positions.
3. Ballast Resistor (Primarily in Conventional Systems): Function: Limits the current flowing through the ignition coil's primary winding during engine operation to prevent overheating and premature coil failure. It is bypassed during starting to provide a higher voltage for easier starting.
4. Ignition Coil: * Function: A to the spark plugs, reducing energy loss and improving reliability. 2.5 Differentiation between Types of Ignition Systems | Feature/System | Conventional Coil Ignition | Transistorised Coil Ignition (TCI) | Electronic Ignition System (EIS) / Distributor-less Ignition (DIS) | | :----------------------- | :--------------------------------------------------------- | :--------------------------------------------------------------- | :----------------------------------------------------------------- | | Primary Current Control | Mechanical contact breaker points | Transistor (triggered by points or a sensor) | Electronic Control Unit (ECU) via sensors | | Distributor | Present (essential for high voltage distribution) | Present (essential for high voltage distribution) | Absent (replaced by individual coil packs) | | Contact Breaker Points | Present (high wear, requires regular adjustment/replacement) | May be present (low wear) or replaced by magnetic/Hall sensor | Absent (fully electronic timing) | | Condenser | Present (to prevent points arcing) | Present (if points are used) or absent (if sensor-based) | Absent | | Maintenance | High (points adjustment/replacement, timing checks) | Medium (less frequent points maintenance if present) | Very Low (virtually maintenance-free) | | Reliability | Lower (due to mechanical wear) | Higher than conventional | Highest (no moving parts for timing, precise control) | | Spark Energy/Voltage | Moderate | Higher than conventional | Highest | | Timing Precision | Less precise (mechanical limitations) | Improved over conventional | Highly precise (ECU control, dynamic adjustment) | | Key Components | Battery, switch, coil, points, condenser, distributor, rotor, cap, HT leads, plugs | Battery, switch, coil, transistor unit, (points/sensor), distributor, rotor, cap, HT leads, plugs | Battery, switch, ECU, CPS, CMP, coil packs, HT leads/COP, plugs | | Examples | Older vehicles, some generator sets | Some 1970s-1980s vehicles | Most modern vehicles (cars, SUVs, trucks) | 3.1 Teacher Activities: Introduction (10 minutes): Begin by asking students what makes a car engine run. Guide them towards the need for ignition. Briefly explain the basic function of the ignition system using a simple analogy (e.g., lighting a gas cooker with a match or sparker). Write the topic and performance objectives on the board.
Explanation of Key Concepts (25 minutes): Present a visual aid (large diagram, chart, or actual components if available) of a conventional ignition system. Systematically explain each major component (battery, switch, coil, distributor assembly, HT leads, spark plug) and its function, pointing to them on the diagram/component. Explain the operating principle of how high voltage is generated and distributed in a conventional system (primary current, magnetic field, points opening, secondary voltage induction, distribution). Introduce the TCI system, highlighting how it differs from conventional (transistor replacing points for switching heavy current). Introduce the Electronic Ignition System (EIS)/DIS, emphasizing the elimination of the distributor and points, the role of sensors (CPS, CMP), ECU, and individual coil packs/COP. Use the comparative table or a similar approach to differentiate between the three types, emphasizing their evolution and advantages.
Demonstration/Visualisation (15 minutes): If actual components are available (e.g., an old distributor, ignition coil, spark plug), show them to the students, allowing them to handle and observe. Demonstrate the basic working principle of a spark plug (if a high-voltage tester is available and safe to use, or use a simpler visual demonstration). Use an animated video or simulation (if projector/computer is available) to show the internal workings of the ignition system, especially the distributor and spark generation.
Activity Facilitation (10 minutes): Divide students into small groups. Provide each group with a simplified diagram of one type of ignition system (unlabeled). Instruct groups to label the components and write down the primary function of each. Circulate among groups, providing clarification and correction.
Q&A and Reinforcement (5 minutes): Address any questions from students.
Summarize the key takeaways: the three types of systems, their main components, and how they differ. 3.2 Student Activities: Active Listening and Note-taking: Students will listen attentively to the teacher's explanations and take comprehensive notes on the types of ignition systems, their components, and functions.
Observation and Identification: Students will observe the diagrams, charts, or actual components presented by the teacher, identifying each part as it is explained.
Group Discussion and Labeling: In their assigned groups, students will discuss and collaborate to label the components on provided unlabeled diagrams of ignition systems and state their functions.
Questioning: Students will ask clarifying questions about the concepts, components, or operational principles they find challenging.
Comparative Analysis: Students will participate in discussions comparing the different ignition systems, highlighting their advantages and disadvantages.
Sketching: Students will practice sketching simplified diagrams of the different ignition systems, showing key components.
Automotive Repair and Maintenance Entrepreneurship: Learners can apply their knowledge to start small-scale auto repair businesses, specializing in ignition system diagnostics and repair. In Nigeria, many vehicles on the road are older models that frequently require maintenance of their conventional or TCI systems. Understanding these systems directly translates into job opportunities for self-employment or working in existing mechanic workshops.
Fuel Efficiency and Vehicle Performance: The knowledge of how ignition systems work directly relates to a vehicle's fuel efficiency and overall performance. A well-maintained ignition system ensures complete combustion, reducing fuel consumption and emissions. This is crucial for vehicle owners looking to save on fuel costs (e.g., commercial drivers like 'Danfo' and 'Keke Napep' operators) and for meeting environmental standards, even if informally enforced.
Vehicle Diagnosis and Troubleshooting: Understanding the functions of each component allows individuals to troubleshoot common vehicle issues such as hard starting, misfires, rough idling, and engine stalls. For example, a student can identify a faulty spark plug by observing its condition or by testing it, a common task for any mechanic dealing with vehicles in Nigerian towns and cities. This empowers them to make informed decisions about vehicle repairs, whether for their personal vehicle or as a professional.