![Car ignition system](https://upload.wikimedia.org/wikipedia/commons/c/cb/Car_ignition_system.svg)
A distributor is an enclosed rotating switch used in
spark-ignition
A spark-ignition engine (SI engine) is an internal combustion engine, generally a petrol engine, where the combustion process of the air-fuel mixture is ignited by a spark from a spark plug. This is in contrast to compression-ignition engines, t ...
internal combustion engine
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...
s that have mechanically timed
ignition
Ignition may refer to:
Science and technology
* Firelighting, the human act of creating a fire for warmth, cooking and other uses
* Combustion, an exothermic chemical reaction between a fuel and an oxidant
* Fusion ignition, the point at which a ...
. The distributor's main function is to route high voltage
current
Currents, Current or The Current may refer to:
Science and technology
* Current (fluid), the flow of a liquid or a gas
** Air current, a flow of air
** Ocean current, a current in the ocean
*** Rip current, a kind of water current
** Current (stre ...
from the
ignition coil
An ignition coil (also called a spark coil) is an induction coil in an automobile's ignition system that transforms the battery's voltage to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel. So ...
to the
spark plugs in the correct
firing order
The firing order of an internal combustion engine is the sequence of ignition for the cylinders.
In a spark ignition (e.g. gasoline/petrol) engine, the firing order corresponds to the order in which the spark plugs are operated. In a diesel engi ...
, and for the correct amount of time. Except in
magneto
A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current. It is categorized as a form of alternator, ...
systems and many modern computer controlled engines that use crank angle/position sensors, the distributor also houses a mechanical or inductive breaker switch to open and close the ignition coil's primary circuit.
The first reliable battery operated ignition was the
Delco ignition system
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 ...
developed by
Dayton Engineering Laboratories Co.
Delco Electronics Corporation was the automotive electronics design and manufacturing subsidiary of General Motors based in Kokomo, Indiana, that manufactured ''Delco'' Automobile radios and other electric products found in GM cars. In 1972, G ...
(Delco) and introduced in the 1910
Cadillac Model 30
The Cadillac Model Thirty is an automobile that was introduced in December 1909 by the Cadillac Division of General Motors, and sold through 1911. It was the company's only model for those years and was based on the 1907 Model G. The 1912 Model ...
. This ignition was developed by
Charles Kettering
Charles Franklin Kettering (August 29, 1876 – November 25, 1958) sometimes known as Charles Fredrick Kettering was an American inventor, engineer, businessman, and the holder of 186 patents.
For the list of patents issued to Kettering, see, Le ...
and was considered a wonder in its day.
Atwater Kent
Arthur Atwater Kent Sr. (December 3, 1873 – March 4, 1949) was an American inventor and prominent radio manufacturer based in Philadelphia. In 1921, he patented the modern form of the automobile ignition coil.
Biography
Arthur Kent was born ...
invented his
Unisparker ignition system about this time in competition with the Delco system. By the end of the 20th century mechanical ignitions were disappearing from
automotive applications in favor of
inductive or
capacitive
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of a c ...
electronic ignition
An ignition system generates a spark or heats an electrode to a high temperature to ignite a fuel-air mixture in spark ignition internal combustion engines, oil-fired and gas-fired boilers, Rocket engine#Ignition, rocket engines, etc. The widest ...
s fully controlled by
engine control units (ECU), rather than directly timed to the engine's
crankshaft
A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecting ...
speed.
Description
A distributor consists of a rotating arm or
rotor
Rotor may refer to:
Science and technology
Engineering
*Rotor (electric), the non-stationary part of an alternator or electric motor, operating with a stationary element so called the stator
* Helicopter rotor, the rotary wing(s) of a rotorcraft ...
inside the distributor cap, on top of the distributor shaft, but insulated from it and the body of the vehicle (
ground). The distributor shaft is driven by a gear on the
camshaft
A camshaft is a shaft that contains a row of pointed cams, in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines (to operate the intake and exhaust valves), mechanically controlled ignition systems ...
on most overhead valve engines, and attached directly to a camshaft on most overhead cam engines. (The distributor shaft may also drive the
oil pump.) The metal part of the rotor contacts the high voltage cable from the ignition coil via a spring-loaded
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
brush
A brush is a common tool with bristles, wire or other filaments. It generally consists of a handle or block to which filaments are affixed in either a parallel or perpendicular orientation, depending on the way the brush is to be gripped durin ...
on the underside of the distributor cap. The metal part of the rotor arm passes close to (but does not touch) the output contacts which connect via
high tension leads
High tension leads or high tension cables or spark plug wires or spark plug cables, colloquially referred to as HT leads, are the wires that connect a distributor, ignition coil, or magneto to each of the spark plugs in some types of internal comb ...
to the
spark plug of each
cylinder
A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base.
A cylinder may also be defined as an infin ...
. As the rotor spins within the distributor, electric current is able to jump the small gaps created between the rotor arm and the contacts due to the high voltage created by the ignition coil.
The distributor shaft has a
cam
Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca2+, and the bin ...
that operates the
contact breaker
A contact breaker (or "points") 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 ...
(also called ''points''). Opening the points causes a high
induction
Induction, Inducible or Inductive may refer to:
Biology and medicine
* Labor induction (birth/pregnancy)
* Induction chemotherapy, in medicine
* Induced stem cells, stem cells derived from somatic, reproductive, pluripotent or other cell t ...
voltage in the system's
ignition coil
An ignition coil (also called a spark coil) is an induction coil in an automobile's ignition system that transforms the battery's voltage to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel. So ...
.
The distributor also houses the
centrifugal advance unit: a set of hinged weights attached to the distributor shaft, that cause the breaker points mounting plate to slightly rotate and advance the spark
timing with higher engine
revolutions per minute
Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines.
Standards
ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...
(rpm). In addition, the distributor has a
vacuum advance unit that advances the timing even further as a function of the vacuum in the
inlet manifold. Usually there is also a
capacitor
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of ...
attached to the distributor. The capacitor is connected
parallel
Parallel is a geometric term of location which may refer to:
Computing
* Parallel algorithm
* Parallel computing
* Parallel metaheuristic
* Parallel (software), a UNIX utility for running programs in parallel
* Parallel Sysplex, a cluster of ...
to the breaker points, to suppress
sparking to prevent excessive wear of the points.
Around the 1970s the primary breaker points were largely replaced with a
Hall effect sensor
A Hall effect sensor (or simply Hall sensor) is a type of sensor which detects the presence and magnitude of a magnetic field using the Hall effect. The output voltage of a Hall sensor is directly proportional to the strength of the field. ...
or optical sensor. As this is a non-contacting device and the ignition coil is controlled by
solid state electronics
Solid-state electronics means semiconductor electronics: electronic equipment using semiconductor devices such as transistors, diodes and integrated circuits (ICs). The term is also used as an adjective for devices in which semiconductor electr ...
, a great amount of maintenance in point adjustment and replacement was eliminated. This also eliminates any problem with breaker follower or cam wear, and by eliminating a side load it extends distributor shaft
bearing life. The remaining secondary (high voltage) circuit stayed essentially the same, using an ignition coil and a rotary distributor.
Most distributors used on electronically fuel injected engines lack vacuum and centrifugal advance units. On such distributors, the timing advance is controlled electronically by the engine computer. This allows more accurate control of ignition timing, as well as the ability to alter timing based on factors other than engine speed and manifold vacuum (such as engine temperature). Additionally, eliminating vacuum and centrifugal advance results in a simpler and more reliable distributor.
Distributor cap
The distributor cap is the cover that protects the distributor's internal parts and holds the contacts between internal rotor and the spark plug wires.
The distributor cap has one post for each cylinder, and in points ignition systems there is a central post for the current from the
ignition coil
An ignition coil (also called a spark coil) is an induction coil in an automobile's ignition system that transforms the battery's voltage to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel. So ...
coming into the distributor. There are some exceptions however, as some engines (many
Alfa Romeo
Alfa Romeo Automobiles S.p.A. () is an Italian luxury car manufacturer and a subsidiary of Stellantis. The company was founded on 24 June 1910, in Milan, Italy. "Alfa" is an acronym of its founding name, "Anonima Lombarda Fabbrica Automobili." ...
cars, some 1980s Nissans) have ''two'' spark plugs per cylinder, so there are two leads coming out of the distributor per cylinder. Another implementation is the
wasted spark
A wasted spark system is a type of ignition system used in some four-stroke cycle internal combustion engines. In a wasted spark system, the spark plugs fire in pairs, with one plug in a cylinder on its compression stroke and the other plug in a ...
system, where a single contact serves two leads, but in that case each lead connects one cylinder. In General Motors
high energy ignition
High energy ignition, also known as H.E.I., is an electronic ignition system designed by the Delco-Remy Division of General Motors. It was used on all GM vehicles, at least in the North American market, from 1975 through the mid-1980s. There wer ...
(HEI) systems there is no central post and the ignition coil sits on top of the distributor. Some Toyota and Honda engines also have their coil within the distributor cap. On the inside of the cap there is a terminal that corresponds to each post, and the plug terminals are arranged around the circumference of the cap according to the
firing order
The firing order of an internal combustion engine is the sequence of ignition for the cylinders.
In a spark ignition (e.g. gasoline/petrol) engine, the firing order corresponds to the order in which the spark plugs are operated. In a diesel engi ...
in order to send the secondary voltage to the proper spark plug at the right time.
The rotor is attached to the top of the distributor shaft which is driven by the engine's
camshaft
A camshaft is a shaft that contains a row of pointed cams, in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines (to operate the intake and exhaust valves), mechanically controlled ignition systems ...
and thus synchronized to it. Synchronization to the camshaft is required as the rotor must turn at exactly half the speed of the main
crankshaft
A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecting ...
in the 4-stroke cycle. Often, the rotor and distributor are attached directly to the end of one of the (or the only) camshaft, at the opposite end to the timing drive belt. This rotor is pressed against a
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
brush
A brush is a common tool with bristles, wire or other filaments. It generally consists of a handle or block to which filaments are affixed in either a parallel or perpendicular orientation, depending on the way the brush is to be gripped durin ...
on the center terminal of the distributor cap which connects to the ignition coil. The rotor is constructed such that the center tab is electrically connected to its outer edge so the current coming in to the center post travels through the carbon point to the outer edge of the rotor. As the camshaft rotates, the rotor spins and its outer edge passes each of the internal plug terminals to fire each spark plug in sequence.
Engines that use a mechanical distributor may fail if they run into deep puddles because any water that gets onto the distributor can short out the electric current that should go through the spark plugs, rerouting it directly to the body of the vehicle. This in turn causes the engine to stop as the fuel is not ignited in the cylinders. This problem can be fixed by removing the distributor's cap and drying the cap, cam, rotor and the contacts by wiping with tissue paper or a clean rag, by blowing hot air on them, or using a moisture displacement spray e.g.
WD-40
WD-40 is an American brand and the trademark of a penetrating oil manufactured by the WD-40 Company based in San Diego, California. The formula for WD-40 was invented for the Rocket Chemical Company as early as 1953 before it evolved into ...
or similar. Oil, dirt or other contaminants can cause similar problems, so the distributor should be kept clean inside and outside to ensure reliable operation. Some engines include a rubber o-ring or gasket between the distributor base and cap to help prevent this problem. The gasket is made of a material like Viton or butyl for a tight seal in extreme temperatures and chemical environments.
This gasket should not be discarded when replacing the cap. Most distributor caps have the position of the number 1 cylinder's terminal molded into the plastic. By referencing a
firing order
The firing order of an internal combustion engine is the sequence of ignition for the cylinders.
In a spark ignition (e.g. gasoline/petrol) engine, the firing order corresponds to the order in which the spark plugs are operated. In a diesel engi ...
diagram and knowing the direction the rotor turns, (which can be seen by cranking the engine with the cap off) the spark plug wires can be correctly routed. Most distributor caps are designed so that they cannot be installed in the wrong position. Some older engine designs allow the cap to be installed in the wrong position by 180 degrees, however. The number 1 cylinder position on the cap should be noted before a cap is replaced.
The distributor cap is a prime example of a component that eventually succumbs to heat and vibration. It is a relatively easy and inexpensive part to replace if its
bakelite
Polyoxybenzylmethylenglycolanhydride, better known as Bakelite ( ), is a thermosetting phenol formaldehyde resin, formed from a condensation reaction of phenol with formaldehyde. The first plastic made from synthetic components, it was developed ...
housing does not break or crack first. Carbon deposit accumulation or erosion of its metal terminals may also cause distributor-cap failure.
As it is generally easy to remove and carry off, the distributor cap can be taken off as a means of theft prevention. Although not practical for everyday use, because it is essential for the starting and running of the engine, its removal thwarts any attempt at
hot-wiring
Hot-wiring is the process of bypassing a motor vehicle's ignition switch and thus starting it without the key. It is often utilized during a vehicle theft. However, a legitimate vehicle owner who has lost a vehicle key or starting a vehicle wit ...
the vehicle.
Direct and distributorless ignition
Modern engine designs have abandoned the high-voltage distributor and coil, instead performing the distribution function in the primary circuit electronically and applying the primary (low-voltage) pulse to individual coils for each spark plug, or one coil for each pair of companion cylinders in an engine (two coils for a four-cylinder, three coils for a six-cylinder, four coils for an eight-cylinder, and so on).
In traditional remote distributorless systems, the coils are mounted together in a
transformer oil Transformer oil or insulating oil is an oil that is stable at high temperatures and has excellent electrical insulating properties. It is used in oil-filled transformers (wet transformers), some types of high-voltage capacitors, fluorescent lamp b ...
filled coil pack, or separate coils for each cylinder, which are secured in a specified place in the engine compartment with wires to the spark plugs, similar to a distributor setup.
General Motors
The General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. It is the largest automaker in the United States and ...
,
Ford
Ford commonly refers to:
* Ford Motor Company, an automobile manufacturer founded by Henry Ford
* Ford (crossing), a shallow crossing on a river
Ford may also refer to:
Ford Motor Company
* Henry Ford, founder of the Ford Motor Company
* Ford F ...
,
Chrysler
Stellantis North America (officially FCA US and formerly Chrysler ()) is one of the " Big Three" automobile manufacturers in the United States, headquartered in Auburn Hills, Michigan. It is the American subsidiary of the multinational automoti ...
,
Hyundai Hyundai is a South Korean industrial conglomerate ("chaebol"), which was restructured into the following groups:
* Hyundai Group, parts of the former conglomerate which have not been divested
** Hyundai Mobis, Korean car parts company
** Hyundai ...
,
Subaru
( or ; ) is the automaker, automobile manufacturing division of Japanese transportation conglomerate (company), conglomerate Subaru Corporation (formerly known as Fuji Heavy Industries), the Automotive industry#By manufacturer, twenty-first ...
,
Volkswagen
Volkswagen (),English: , . abbreviated as VW (), is a German Automotive industry, motor vehicle manufacturer headquartered in Wolfsburg, Lower Saxony, Germany. Founded in 1937 by the German Labour Front under the Nazi Party and revived into a ...
and
Toyota
is a Japanese multinational automotive manufacturer headquartered in Toyota City, Aichi, Japan. It was founded by Kiichiro Toyoda and incorporated on . Toyota is one of the largest automobile manufacturers in the world, producing about 10 ...
are among the automobile manufacturers known to have used coil packs. Coil packs by Delco for use with General Motors engines allow removal of the individual coils in case one should fail, but in most other remote distributorless coil pack setups, if a coil were to fail, replacement of the whole pack would be required to fix the problem.
More recent layouts utilize a coil located very near to each spark plug known as ''coil-near-plugs'', or directly on top of each spark plug known as ''direct ignition'' (''DI'') or ''coil-on-plug'' (''COP''). This design avoids the need to transmit very high voltages, which is often a source of trouble, especially in damp conditions.
Both direct and remote distributorless systems also allow finer levels of ignition control by the engine computer, which helps to increase power output, decrease fuel consumption and emissions, and implement features such as
cylinder deactivation Variable displacement is an automobile engine technology that allows the engine displacement to change, usually by deactivating cylinders, for improved fuel economy. The technology is primarily used in large, multi-cylinder engines. Many automobile ...
.
Spark plug wires, which need routine replacement due to degradation, are also eliminated when the individual coils are mounted directly on top of each plug, since the high voltages and fields exist only over a very short distance from the coil to the plug.
Wasted spark
The distributor can be eliminated on four-stroke engines by using the wasted spark principle. An ignition pulse is delivered to two cylinders at the same time,chosen so that one cylinder is in an exhaust stroke while the other is about to begin the power stroke. The spark in the cylinder on the exhaust phase is wasted. Each end of the ignition coil winding is connected to a spark plug and they fire in pairs.
A single-cylinder engine has only one spark plug and so needs no distributor. Ignition systems on such engines may produce a wasted spark during the exhaust stroke.
See also
*
Saab Direct Ignition
Saab Direct Ignition is a capacitor discharge ignition developed by Saab Automobile, then known as Saab-Scania, and '' Mecel AB'' during the 1980s.
It was first shown in 1985 and put into series production in the Saab 9000 in 1988. One of the fi ...
*
Timing mark
A timing mark is an indicator used for setting the timing of the ignition system of an engine, typically found on the crankshaft pulley (as pictured) or the flywheel, being the largest radius rotating at crankshaft speed and therefore the place w ...
References
External links
{{Authority control
Electric power distribution
Engine components
Ignition systems