Starter ring gear
Encyclopedia
A starter ring gear, sometimes called a starter ring or ring gear
, is a medium carbon steel
ring with teeth that is fitted on the periphery of a flexplate or flywheel
of an internal combustion engine
, mostly for automotive applications.
The teeth of the starter ring are driven by the smaller gear (the pinion
) of the starter motor. The primary function of the starter ring is to transfer torque
from the starter motor pinion to the flywheel or flexplate to rotate the engine to begin the cycle.
The starter ring gear is most commonly made by forming a length of square or rectangular steel bar into a circle and welding the ends together. There then follow various heat-treatment like normalising, tempering and machining operations, including the machining of the teeth and finally a heat-treatment operation. The teeth of the starter ring need to be hardened in order to increase their strength and resist wear. The normal hardness at pitch circle diameter is 45-55 HRC. The hardness at the root of the teeth is about 40 HRC and at 2 mm below root the hardness is 35 Hrc max. The body of the ring is generally left untreated.
Engines with manual transmission
usually have a heavy flywheel, typically 5 to 10 kg
of cast iron
, with the starter ring gear shrunk onto the outside. This is done by heating the ring to around 200 °C
to expand the ring which is then placed onto the flywheel, often held in firmly against a location shoulder until cool. The interference fit renders the starter ring firmly attached to the flywheel.
Engines with automatic transmission
s instead have a pressed steel plate with the starter ring gear usually welded
onto the outside of the plate.
Gear
A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....
, is a medium carbon steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
ring with teeth that is fitted on the periphery of a flexplate or flywheel
Flywheel
A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...
of an internal combustion engine
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
, mostly for automotive applications.
The teeth of the starter ring are driven by the smaller gear (the pinion
Pinion
A pinion is a round gear used in several applications:*usually the smallest gear in a gear drive train, although in the case of John Blenkinsop's Salamanca, the pinion was rather large...
) of the starter motor. The primary function of the starter ring is to transfer torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
from the starter motor pinion to the flywheel or flexplate to rotate the engine to begin the cycle.
The starter ring gear is most commonly made by forming a length of square or rectangular steel bar into a circle and welding the ends together. There then follow various heat-treatment like normalising, tempering and machining operations, including the machining of the teeth and finally a heat-treatment operation. The teeth of the starter ring need to be hardened in order to increase their strength and resist wear. The normal hardness at pitch circle diameter is 45-55 HRC. The hardness at the root of the teeth is about 40 HRC and at 2 mm below root the hardness is 35 Hrc max. The body of the ring is generally left untreated.
Engines with manual transmission
Transmission (mechanics)
A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines transmission as: an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a...
usually have a heavy flywheel, typically 5 to 10 kg
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
of cast iron
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...
, with the starter ring gear shrunk onto the outside. This is done by heating the ring to around 200 °C
Celsius
Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
to expand the ring which is then placed onto the flywheel, often held in firmly against a location shoulder until cool. The interference fit renders the starter ring firmly attached to the flywheel.
Engines with automatic transmission
Automatic transmission
An automatic transmission is one type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears manually...
s instead have a pressed steel plate with the starter ring gear usually welded
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
onto the outside of the plate.