Ignition systems have undergone significant advancements, especially with the integration of sophisticated electronics. However, the core principles of modern systems still trace back to the original coil ignition systems introduced over a century ago. At the heart of this technology lies the Ignition Coil Function, a crucial process for starting your gasoline-powered vehicle.
The pioneering coil-based ignition system is attributed to Charles Kettering, an American inventor. Around 1910/1911, Kettering developed this system for a major automobile manufacturer, marking a significant leap forward. His innovation was the first electrical system to simultaneously power both the starter motor and the ignition. By incorporating a battery, a generator, and a more comprehensive electrical system, Kettering ensured a stable electrical supply to the ignition coil.
The Kettering system, illustrated in Figure 1, employed a single ignition coil to generate a high voltage. This high voltage was then directed to a rotor arm within the distributor assembly. The rotor arm, acting like a rotating switch, pointed the voltage to a series of electrical contacts – one for each cylinder in the engine. These contacts were connected via spark plug wires to the spark plugs, ensuring the high voltage was delivered to each cylinder in the correct firing order.
Figure 1: Diagram illustrating the key components of the original Kettering ignition system, highlighting the single coil, distributor, and connections to spark plugs.
The Kettering ignition system became the dominant ignition technology for mass-produced gasoline cars, maintaining its position until the 1970s and 1980s. It was during this period that electronically switched and controlled ignition systems began to supersede these mechanical predecessors.
The Fundamental Principle Behind Ignition Coil Function
Ignition coils are ingeniously designed to produce the extremely high voltages necessary to create a spark at the spark plug. This crucial ignition coil function relies on the fundamental relationship between electricity and magnetism.
When an electric current flows through a conductor, like a coil of wire, it generates a magnetic field around that coil, as depicted in Figure 2. This magnetic field, or more accurately, magnetic flux, effectively stores energy. This stored energy can later be converted back into electrical energy when needed.
Figure 2: Illustration demonstrating how an electric current passing through a wire coil creates a surrounding magnetic field, essential to the ignition coil function.
Initially, when the electric current is switched on, it rapidly increases to its maximum level. Simultaneously, the magnetic field strengthens and expands, reaching its peak when the current stabilizes. Conversely, when the electric current is switched off, the magnetic field collapses inwards towards the coil of wire.
Two primary factors influence the strength of this magnetic field:
- Current Strength: Increasing the electric current applied to the coil of wire directly strengthens the magnetic field.
- Number of Windings: A higher number of windings in the coil also results in a stronger magnetic field.
Inducing Electric Current: Harnessing a Changing Magnetic Field
A key aspect of ignition coil function is the principle of inductance. If a coil of wire is placed within a magnetic field, and that magnetic field changes or moves, it induces an electric current within the coil of wire. This phenomenon is known as ‘inductance’.
A simple demonstration of this principle involves moving a permanent magnet across a coil. This movement, or change in the magnetic field, induces an electric current in the coil wire, as shown in Figure 3.
Figure 3: Diagram illustrating the principle of inductance, where movement of a magnet near a coil of wire generates an electric current within the coil.
The magnitude of voltage induced in the coil is determined by two main factors:
- Rate and Strength of Magnetic Field Change: The faster the change or movement of the magnetic field, and the greater the change in its strength, the higher the induced voltage.
- Number of Coil Windings: Increasing the number of windings in the coil also increases the induced voltage.
Utilizing a Collapsing Magnetic Field for Voltage Induction
In the context of ignition coil function, a collapsing magnetic field is crucial for generating the high voltage spark. When a magnetic field is created by passing an electric current through a coil, any change in this current (increase or decrease) will cause a corresponding change in the magnetic field. Specifically, when the electric current is switched off, the magnetic field collapses. This collapsing magnetic field then induces an electric current within the same coil, as illustrated in Figure 4.
Figure 4: Illustration of a collapsing magnetic field inducing an electric current in the coil after the initial current is switched off, a fundamental aspect of ignition coil operation.
Similar to how increasing the speed of movement of a magnetic field enhances induced voltage, a more rapid collapse of the magnetic field will also induce a higher voltage. Furthermore, increasing the number of windings in the coil also contributes to a higher induced voltage.
Mutual Inductance and Transformer Action: Amplifying Voltage
Ignition coil function leverages ‘mutual inductance’ and ‘transformer action’ to achieve the necessary high voltage. If two coils of wire are positioned close to each other – one designated as the primary winding and the other as the secondary winding – and an electric current is used to create a magnetic field around the primary winding, this magnetic field will also encompass the secondary winding. When the electric current to the primary winding is switched off, and the magnetic field collapses, it induces a voltage in both the primary and secondary windings. This interaction is known as ‘mutual inductance’, depicted in Figure 5.
Figure 5: Diagram showing mutual inductance between primary and secondary windings, where the magnetic field of the primary coil affects the secondary coil.
In ignition coils, and many electrical transformers, the secondary winding is designed with significantly more windings than the primary winding. Consequently, when the magnetic field collapses, it induces a much higher voltage in the secondary winding compared to the primary winding, as shown in Figure 6.
Figure 6: Illustration highlighting the difference in windings between primary and secondary coils, demonstrating how this difference amplifies voltage in the secondary coil during magnetic field collapse.
Typically, an ignition coil’s primary winding contains around 150 to 300 turns of wire, while the secondary winding can have between 15,000 to 30,000 turns – approximately 100 times more.
The magnetic field is initially generated when the vehicle’s electrical system applies approximately 12 volts to the ignition coil’s primary winding. When a spark is required at a spark plug, the ignition system interrupts the current flow to the primary winding, causing the magnetic field to collapse. This collapsing magnetic field induces a voltage in the primary winding, around 200 volts. However, due to the higher number of windings in the secondary coil, the voltage induced in the secondary winding is amplified roughly 100 times, reaching approximately 20,000 volts.
Therefore, by employing mutual inductance and a secondary winding with significantly more turns than the primary winding, ignition coil function effectively transforms a low voltage supply into the very high voltage required for spark ignition. This voltage amplification process is referred to as ‘transformer action’.
To further enhance efficiency, ignition coils incorporate an iron core around which the primary and secondary windings are wrapped. This iron core concentrates and strengthens the magnetic field and flux, improving the overall performance of the ignition coil.
DENSO stands as a long-established leader in direct ignition technology, offering a wide range of high-quality ignition coils in the aftermarket. Learn more about DENSO Ignition Coils and their advantages.
