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The Delco ignition system, also known as the Kettering ignition system, points and condenser ignition or breaker point ignition, is a type of inductive discharge ignition system invented by Charles F. Kettering. It was first sold commercially on the 1912 Cadillac [1] and was manufactured by Delco. Over time, it was used extensively by all automobile and truck manufacturers on spark ignition, i.e., gasoline engines. Today it is still widely used in coil-on-plug, coil-near-plug and in coil packs in distributorless ignitions. [2] An alternative system used in automobiles is capacitor discharge ignition, primarily found now as aftermarket upgrade systems. [3] Electronic ignition was a common term for Kettering inductive ignition with the points (mechanical switch) replaced with an electronic switch such as a transistor. [4]
On initial starting, a storage battery is connected through the ignition switch (called "Contactor" in the figure above). Once the engine is running, an engine-driven alternator or generator provides electrical power.
The breaker points (called "Contact breaker" in the figure) are an electrical switch opened and closed by a cam on the distributor shaft. This is timed so the points are closed for the majority of the engine cycle, allowing current to flow through the ignition coil, and are opened momentarily when a spark is desired.
The ignition coil is a transformer. The primary winding (called the low-tension winding in early texts) is connected to the battery voltage when the points are closed. Due to the inductance of the coil, the current in this circuit builds gradually. This current creates a magnetic field in the coil, which stores a quantity of energy. When the points open, the current maintaining the magnetic field stops and the field collapses. Its stored energy is then returned to the two windings as electromotive force. The primary winding has a small number of turns and by Faraday's law of induction has a voltage spike develop across it of the order of 250 volts. [5] The secondary winding has of the order of 100 times the number of turns as the primary winding, so develops a voltage spike of the order of 25,000 volts. This voltage is high enough to cause a spark to jump across the electrodes of the spark plug. Either polarity voltage spike may be used, but the spark is most efficiently initiated by a negative polarity pulse to the centre of the spark plug. That also lengthens the life of the spark plug.
There is a capacitor (called a condenser in earlier texts) connected across the points. The capacitor absorbs the voltage spike developed in the primary coil when the points open. This prevents an electrical arc from forming at the newly opened contacts on the points and thus prevents rapid erosion of these contacts.
The distributor rotor turns in time with the camshaft. When it is time for a spark plug to fire, the rotor (the blue bar shown in the distributor in the figure above) connects the center electrode of the distributor cap to an electrode connected to a spark plug wire. This occurs simultaneously with the points opening and the coil delivering a high voltage to the center electrode.
Not shown in this diagram is the ballast resistor, which was included in Kettering's patent. [6] It is placed in the primary circuit. The inductance of the primary winding limits the speed at which the current through it can increase to the necessary level to provide enough energy to create a spark. Lowering the inductance of the primary winding allows the current to increase faster, but would lead to a higher maximum current that will shorten the life of the points and increase heating of the coil. The ballast resistor placed in series with the primary winding creates a voltage drop proportional to the current. When the points initially close, current is low so voltage drop across the resistor is low and most of the battery voltage acts across the coil. Once current builds up, voltage drop across the resistor increases, leaving less battery voltage across the coil which limits the maximum current.
Kettering ignitions often had the ignition switch bypass the ballast resistor when in the start position. During starting the battery voltage drops, and bypassing this resistor allows a higher voltage across the coil so more energy could be delivered.
One problem with this design is that, even with a properly sized capacitor, there will be some arcing at the points. Arcing causes the points to "burn." This in turn introduces resistance at the point contacts that reduces primary current and resulting spark intensity. A second problem involves the mechanical cam-follower block that rides on the distributor cam and opens the points. The block wears over time, reducing how much the points open (the "point gap") and causing a corresponding change in both the ignition timing and the fraction of time during which the points are closed. Tune-ups for older vehicles usually involve replacing the points and condenser and setting the gap to factory specifications. A third problem involves the distributor cap and rotor. These components can develop conductive "sneak paths" on their surfaces (also called 'tracking') across which the coil's secondary voltage produces a current, often in the form of an arc, that bypasses the spark plug. When sneak paths develop, the only remedy is replacement of the cap and/or rotor. A fourth problem can arise when one or more of an engine's spark plugs becomes "fouled." Fouling, caused by combustion-byproducts that form deposits on a spark plug's internal insulator, creates an electrically conductive path that dissipates the coil's energy before its secondary voltage can rise high enough to produce a spark. So-called capacitive discharge ignition systems create coil voltages with much shorter rise times and can produce a spark across spark plugs with some fouling.
Electronic ignition systems replace some or all of the components the Delco ignition system with solid state and/or optical devices and provide both higher voltages and more reliable ignition.
An ignition magneto is an older type of ignition system used in spark-ignition engines. It uses a magneto and a transformer to make pulses of high voltage for the spark plugs. The older term "high-tension" means "high-voltage".
A Tesla coil is an electrical resonant transformer circuit designed by inventor Nikola Tesla in 1891. It is used to produce high-voltage, low-current, high-frequency alternating-current electricity. Tesla experimented with a number of different configurations consisting of two, or sometimes three, coupled resonant electric circuits.
A spark plug is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air mixture by an electric spark, while containing combustion pressure within the engine. A spark plug has a metal threaded shell, electrically isolated from a central electrode by a ceramic insulator. The central electrode, which may contain a resistor, is connected by a heavily insulated wire to the output terminal of an ignition coil or magneto. The spark plug's metal shell is screwed into the engine's cylinder head and thus electrically grounded. The central electrode protrudes through the porcelain insulator into the combustion chamber, forming one or more spark gaps between the inner end of the central electrode and usually one or more protuberances or structures attached to the inner end of the threaded shell and designated the side, earth, or ground electrode(s).
An induction coil or "spark coil" is a type of electrical transformer used to produce high-voltage pulses from a low-voltage direct current (DC) supply. To create the flux changes necessary to induce voltage in the secondary coil, the direct current in the primary coil is repeatedly interrupted by a vibrating mechanical contact called an interrupter. Invented in 1836 by the Irish-Catholic priest Nicholas Callan, with additional research by Charles Grafton Page and others, the induction coil was the first type of transformer. It was widely used in x-ray machines, spark-gap radio transmitters, arc lighting and quack medical electrotherapy devices from the 1880s to the 1920s. Today its only common use is as the ignition coils in internal combustion engines and in physics education to demonstrate induction.
A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the potential difference between the conductors exceeds the breakdown voltage of the gas within the gap, a spark forms, ionizing the gas and drastically reducing its electrical resistance. An electric current then flows until the path of ionized gas is broken or the current reduces below a minimum value called the "holding current". This usually happens when the voltage drops, but in some cases occurs when the heated gas rises, stretching out and then breaking the filament of ionized gas. Usually, the action of ionizing the gas is violent and disruptive, often leading to sound, light, and heat.
Ignition systems are used by heat engines to initiate combustion by igniting the fuel-air mixture. In a spark ignition versions of the internal combustion engine, the ignition system creates a spark to ignite the fuel-air mixture just before each combustion stroke. Gas turbine engines and rocket engines normally use an ignition system only during start-up.
A contact breaker is a type of electrical switch, found in the ignition systems of spark-ignition internal combustion engines. The switch is automatically operated by a cam driven by the engine. The timing of operation of the switch is set so that a spark is produced at the right time to ignite the compressed air/fuel mixture in the cylinder of the engine. A mechanism may be provided to slightly adjust timing to allow for varying load on the engine. Since these contacts operate frequently, they are subject to wear, causing erratic ignition of the engine. More recent engines use electronic means to trigger the spark, which eliminated contact wear and allows computer control of ignition timing.
A distributor is an electric and mechanical device used in the ignition system of older spark ignition engines. The distributor's main function is to route electricity from the ignition coil to each spark plug at the correct time.
A spark-gap transmitter is an obsolete type of radio transmitter which generates radio waves by means of an electric spark. Spark-gap transmitters were the first type of radio transmitter, and were the main type used during the wireless telegraphy or "spark" era, the first three decades of radio, from 1887 to the end of World War I. German physicist Heinrich Hertz built the first experimental spark-gap transmitters in 1887, with which he proved the existence of radio waves and studied their properties.
Inrush current, input surge current, or switch-on surge is the maximal instantaneous input current drawn by an electrical device when first turned on. Alternating-current electric motors and transformers may draw several times their normal full-load current when first energized, for a few cycles of the input waveform. Power converters also often have inrush currents much higher than their steady-state currents, due to the charging current of the input capacitance. The selection of over-current-protection devices such as fuses and circuit breakers is made more complicated when high inrush currents must be tolerated. The over-current protection must react quickly to overload or short-circuit faults but must not interrupt the circuit when the inrush current flows.
An ignition coil is used in the ignition system of a spark-ignition engine to transform the battery voltage to the much higher voltages required to operate the spark plug(s). The spark plugs then use this burst of high-voltage electricity to ignite the air-fuel mixture.
An electrical ballast is a device placed in series with a load to limit the amount of current in an electrical circuit.
In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term still encountered in a few compound names, such as the condenser microphone. It is a passive electronic component with two terminals.
Capacitor discharge ignition (CDI) or thyristor ignition is a type of automotive electronic ignition system which is widely used in outboard motors, motorcycles, lawn mowers, chainsaws, small engines, turbine-powered aircraft, and some cars. It was originally developed to overcome the long charging times associated with high inductance coils used in inductive discharge ignition (IDI) systems, making the ignition system more suitable for high engine speeds. The capacitive-discharge ignition uses capacitor to discharge current to the ignition coil to fire the spark plugs.
A flyback diode is any diode connected across an inductor used to eliminate flyback, which is the sudden voltage spike seen across an inductive load when its supply current is suddenly reduced or interrupted. It is used in circuits in which inductive loads are controlled by switches, and in switching power supplies and inverters.
Capacitors have many uses in electronic and electrical systems. They are so ubiquitous that it is rare that an electrical product does not include at least one for some purpose. Capacitors allow only AC signals to pass when they are charged blocking DC signals. The main components of filters are capacitors. Capacitors have the ability to connect one circuit segment to another. Capacitors are used by Dynamic Random Access Memory (DRAM) devices to represent binary information as bits.
Spark plug wires are electrical cables used by older internal combustion engines to transmit high-voltage electricity from the distributor to the spark plugs. Tension in this instance is a synonym for voltage. High tension may also be referred to as HT.
Inductive discharge ignition systems were developed in the 19th century as a means to ignite the air–fuel mixture in the combustion chamber of internal combustion engines. The first versions were low tension coils, then low-tension and in turn high-tension magnetos, which were offered as a more effective alternative to the older-design hot-tube ignitors that had been utilized earlier on hot tube engines. With the advent of small stationary engines; and with the development of the automobile, engine-driven tractors, and engine-driven trucks; first the magneto and later the distributor-type systems were utilized as part of an efficient and reliable engine ignition system on commercially available motorized equipment. These systems were in widespread use on all cars and trucks through the 1960s. Manufacturers such as Ford, General Motors, Chrysler, Citroen, Mercedes, John Deere, International Harvester, and many others incorporated them into their products. The inductive discharge system is still extensively used today.
A trembler coil, buzz coil or vibrator coil is a type of high-voltage ignition coil used in the ignition system of early automobiles, most notably the Benz Patent-Motorwagen and the Ford Model T. Its distinguishing feature is a vibrating magnetically-activated contact called a trembler or interrupter, which breaks the primary current, generating multiple sparks during each cylinder's power stroke. Trembler coils were first used on the 1886 Benz automobile, and were used on the Model T until 1927.
An alternator is a type of electric generator used in modern automobiles to charge the battery and to power the electrical system when its engine is running.