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A starter (also self-starter, cranking motor, or starter motor) is a device used to rotate (crank) an internal-combustion engine so as to initiate the engine's operation under its own power. Starters can be electric, pneumatic, or hydraulic. The starter can also be another internal-combustion engine in the case, for instance, of very large engines, or diesel engines in agricultural or excavation applications.[1]
Internal combustion engines are feedback systems, which, once started, rely on the inertia from each cycle to initiate the next cycle. In a four-stroke engine, the third stroke releases energy from the fuel, powering the fourth (exhaust) stroke and also the first two (intake, compression) strokes of the next cycle, as well as powering the engine's external load. To start the first cycle at the beginning of any particular session, the first two strokes must be powered in some other way than from the engine itself. The starter motor is used for this purpose and it is not required once the engine starts running and its feedback loop becomes self-sustaining.
Before the advent of the starter motor, engines were started by various methods including wind-up springs, gunpowder cylinders, and human-powered techniques such as a removable crank handle which engaged the front of the crankshaft, pulling on an airplane propeller, or pulling a cord that was wound around an open-face pulley.
The hand-crank method was commonly used to start engines, but it was inconvenient, difficult, and dangerous. The behavior of an engine during starting is not always predictable. The engine can kick back, causing sudden reverse rotation. Many manual starters included a one-directional slip or release provision so that once engine rotation began, the starter would disengage from the engine. In the event of a kickback, the reverse rotation of the engine could suddenly engage the starter, causing the crank to unexpectedly and violently jerk, possibly injuring the operator. For cord-wound starters, a kickback could pull the operator towards the engine or machine, or swing the starter cord and handle at high speed around the starter pulley. Even though cranks had an overrun mechanism, when the engine started, the crank could begin to spin along with the crankshaft and potentially strike the person cranking the engine. Additionally, care had to be taken to retard the spark in order to prevent backfiring; with an advanced spark setting, the engine could kick back (run in reverse), pulling the crank with it, because the overrun safety mechanism works in one direction only.
In 1911, Charles F. Kettering, with Henry M. Leland, of Dayton Engineering Laboratories Company (DELCO), invented and filed U.S. Patent 1,150,523 for an electric starter in America. (Kettering had replaced the hand crank on NCR's cash registers with an electric motor five years earlier.)
One aspect of the invention lay in the realization that a relatively small motor, driven with higher voltage and current than would be feasible for continuous operation, could deliver enough power to crank the engine for starting. At the voltage and current levels required, such a motor would burn out in a few minutes of continuous operation, but not during the few seconds needed to start the engine. The starters were first installed on the Cadillac Model Thirty in 1912, with the same system being adopted by Lanchester later that year.[4] These starters also worked as generators once the engine was running, a concept that is now being revived in hybrid vehicles.
Although the electric starter motor was to come to dominate the car market, in 1912, there were several competing types of starter,[4] with the Adams, S.C.A.T. and Wolseley cars having direct air starters, and Sunbeam introducing an air starter motor with similar approach to that used for the Delco and Scott-Crossley electrical starter motors (i.e. engaging with a toothed ring on the flywheel). The Star and Adler cars had spring motors (sometimes referred to as clockwork motors), which used the energy stored in a spring driving through a reduction gear. If the car failed to start, the starter handle could be used to wind up the spring for a further attempt.
One of the innovations on the first Dodge car, the Model 30-35 at its introduction in 1914 was an electric starter and electric lighting with a 12-volt system (against the six volts that was usual at the time) as a standard fitment on what was a relatively low-priced car. The Dodge used a combined starter-generator unit, with a direct current dynamo permanently coupled by gears to the engine's crankshaft. A system of electrical relays allowed this to be driven as a motor to rotate the engine for starting, and once the starter button was released the controlling switchgear returned the unit to operation as a generator. Because the starter-generator was directly coupled to the engine it did not need a method of engaging and disengaging the motor drive. It thus suffered negligible mechanical wear and was virtually silent in operation. The starter-generator remained a feature of Dodge cars until 1929. The disadvantage of the design was that, as a dual-purpose device, the unit was limited in both its power as a motor and its output as a generator, which became a problem as engine size and electrical demands on cars increased. Controlling the switch between motor and generator modes required dedicated and relatively complex switchgear which was more prone to failure than the heavy-duty contacts of a dedicated starter motor. While the starter-generator dropped out of favour for cars by the 1930s, the concept was still useful for smaller vehicles and was taken up by the German firm SIBA Elektrik which built similar system intended mostly for use on motorcycles, scooters, economy cars (especially those will small-capacity two-stroke engines), and marine engines. These were marketed under the 'Dynastart' name. Since motorcycles usually had small engines and limited electrical equipment, as well as restricted space and weight, the Dynastart was a useful feature. The windings for the starter-generator were usually incorporated into the engine's flywheel, thus not requiring a separate unit at all.
The Ford Model T relied on hand cranks until 1919; during the 1920s, electric starters became near-universal on most new cars, making it easier for women and elderly people to drive. It was still common for cars to be supplied with starter handles into the 1960s, and this continued much later for some makes (e.g. Citroën 2CV until end of production in 1990). In many cases, cranks were used for setting timing rather than starting the engine as growing displacements and compression ratios made this impractical. Communist bloc cars such as Ladas often still sported crank-starting as late as the 1980s.
Before Chrysler's 1949 innovation of the key-operated combination ignition-starter switch,[5] the starter was often operated by the driver pressing a button mounted on the floor or dashboard. Some vehicles had a pedal in the floor that manually engaged the starter drive pinion with the flywheel ring gear, then completed the electrical circuit to the starter motor once the pedal reached the end of its travel. Ferguson tractors from the 1940s, including the Ferguson TE20, had an extra position on the gear lever that engaged the starter switch, ensuring safety by preventing the tractors from being started in gear.[6]
The electric starter motor or cranking motor is the most common type used on gasoline engines and small diesel engines. The modern starter motor is either a permanent-magnet or a series-parallel wound direct current electric motor with a starter solenoid (similar to a relay) mounted on it. When DC power from the starting battery is applied to the solenoid, usually through a key-operated switch (the "ignition switch"), the solenoid engages a lever that pushes out the drive pinion on the starter driveshaft and meshes the pinion with the starter ring gear on the flywheel of the engine.[7]
The solenoid also closes high-current contacts for the starter motor, which begins to turn. Once the engine starts, the key-operated switch is opened, a spring in the solenoid assembly pulls the pinion gear away from the ring gear, and the starter motor stops. The starter's pinion is clutched to its drive shaft through an overrunning sprag clutch which permits the pinion to transmit drive in only one direction. In this manner, drive is transmitted through the pinion to the flywheel ring gear, but if the pinion remains engaged (as for example because the operator fails to release the key as soon as the engine starts, or if there is a short and the solenoid remains engaged), the pinion will spin independently of its drive shaft. This prevents the engine driving the starter, for such backdrive would cause the starter to spin so fast as to fly apart.
The sprag clutch arrangement would preclude the use of the starter as a generator if employed in the hybrid scheme mentioned above, unless modifications were made. The standard starter motor is typically designed for intermittent use, which would preclude its use as a generator. The starter's electrical components are designed only to operate for typically under 30 seconds before overheating (by too-slow dissipation of heat from ohmic losses), to save weight and cost. Most automobile owner manuals instruct the operator to pause for at least ten seconds after each ten or fifteen seconds of cranking the engine, when trying to start an engine that does not start immediately.
This overrunning-clutch pinion arrangement was phased into use beginning in the early 1960s; before that time, a Bendix drive was used. The Bendix system places the starter drive pinion on a helically cut drive shaft. When the starter motor begins turning, the inertia of the drive pinion assembly causes it to ride forward on the helix and thus engage with the ring gear. When the engine starts, backdrive from the ring gear causes the drive pinion to exceed the rotative speed of the starter, at which point the drive pinion is forced back down the helical shaft and thus out of mesh with the ring gear.[8] This has the disadvantage that the gears will disengage if the engine fires briefly but does not continue to run.
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