Starter Motor

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. Among these methods, the hand-crank method was most commonly used to start engines, but it was inconvenient, difficult, and dangerous. The Ford Model T relied on hand cranks until 1919.



The first electric starter was installed on an Arnold, built in 1896, by electrical engineer H. J. Dowsing. In 1903, Clyde Coleman invented and patented the first electric starter in America. During the 1920s, electric starters became near-universal on most new cars, making it easier for women and elderly people to drive.

In 1949 Chrysler introduced the key-operated combination ignition-starter switch. Prior to this innovation, 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.



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.



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.



This overrunning-clutch pinion arrangement was phased into use beginning in the early 1960s. Before that time, a Bendix drive was used. In intermediate development between the Bendix drive developed in the 1930s and the overrunning-clutch designs introduced in the 1960s, was the Bendix Folo-Thru drive. The standard Bendix drive would disengage from the ring gear as soon as the engine fired, even if it did not continue to run. The Folo-Thru drive contained a latching mechanism and a set of flyweights in the body of the drive unit. When the starter motor begins turning and the drive unit is forced forward on the helical shaft by inertia, it is latched into the engaged position. Only once the drive unit is spun at a speed higher than that attained by the starter motor itself (i.e., it is back driven by the running engine) will the flyweights pull radially outward, releasing the latch and permitting the over driven drive unit to be spun out of engagement.

In 1962, Chrysler introduced a starter incorporating a gear train between the motor and the drive shaft. The motor shaft included integrally cut gear teeth forming a pinion that meshes with a larger adjacent driven gear to provide a gear reduction ratio of 3.75:1. This permitted the use of a higher-speed, lower-current, lighter and more compact motor assembly while increasing cranking torque. Variants of this starter design were used on most rear- and four-wheel-drive vehicles produced by Chrysler Corporation from 1962 through 1987. The Chrysler gear-reduction starter formed the conceptual basis for the gear-reduction starters that now predominate in vehicles on the road..

Those starters not employing offset gear trains like the Chrysler unit generally employ planetary epicyclic gear trains instead. Ford issued a non-standard starter, a direct-drive "movable pole shoe" design that provided cost reduction rather than electrical or mechanical benefits. This type of starter eliminated the solenoid, replacing it with a movable pole shoe and a separate starter relay. Direct-drive starters are almost entirely obsolete owing to their larger size, heavier weight and higher current requirements.