Herringbone gear
Encyclopedia
A herringbone gear, also known as a double helical gear, is a special type of gear
which is a side to side (not face to face) combination of two helical gears of opposite hands. Unlike helical gears they can sustain axial load smoothly. From the top the helical grooves of this gear looks like letter V.
Like helical gears, they have the advantage of transferring power smoothly as multiple gear teeth engage and disengage simultaneously. Their advantage over the helical gears is that the side-thrust of one half is balanced by that of the other half. This means that herringbone gears can be used in torque gearboxes without requiring a substantial thrust bearing
. Because of this herringbone gears were an important step in the introduction of the steam turbine
to marine propulsion.
Precision herringbone gears are more difficult to manufacture than equivalent spur or helical gears and consequently are more expensive.
They are used in heavy machinery.
Where the oppositely angled teeth meet in the middle of a herringbone gear, the alignment may be such that tooth tip meets tooth tip, or the alignment may be staggered, so that tooth tip meets tooth trough. The latter alignment is the unique defining characteristic of a Wuest type herringbone gear, named after its inventor.
With the older method of fabrication, herringbone gears had a central channel separating the two oppositely-angled courses of teeth. This was necessary to permit the shaving tool to run out of the groove. The development of the Sykes gear shaper
made it possible to have continuous teeth, with no central gap. After the W.E. Sykes and Farrel Gear Machine companies dissolved in 1983-84 there are no current production machines that have this ability. It is standard industry practice to obtain an older machine and rebuild it if necessary to create this unique type of gear. A disadvantage of the herringbone gear is that it cannot be cut by simple gear hobbing machines, as the cutter would run into the other half of the gear. Solutions to this have included assembling small gears by stacking two helical gears together, cutting the gears with a central groove to provide clearance, and (particularly in the early days) by casting the gears to an accurate pattern and without further machining.
The logo of the car maker Citroën
is a graphic representation of a herringbone gear, it comes from André Citroën
's early involvement in the manufacture of these gears.
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....
which is a side to side (not face to face) combination of two helical gears of opposite hands. Unlike helical gears they can sustain axial load smoothly. From the top the helical grooves of this gear looks like letter V.
Like helical gears, they have the advantage of transferring power smoothly as multiple gear teeth engage and disengage simultaneously. Their advantage over the helical gears is that the side-thrust of one half is balanced by that of the other half. This means that herringbone gears can be used in torque gearboxes without requiring a substantial thrust bearing
Thrust bearing
A thrust bearing is a particular type of rotary bearing. Like other bearings they permit rotation between parts, but they are designed to support a high axial load while doing this.Thrust bearings come in several varieties....
. Because of this herringbone gears were an important step in the introduction of the steam turbine
Steam turbine
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....
to marine propulsion.
Precision herringbone gears are more difficult to manufacture than equivalent spur or helical gears and consequently are more expensive.
They are used in heavy machinery.
Where the oppositely angled teeth meet in the middle of a herringbone gear, the alignment may be such that tooth tip meets tooth tip, or the alignment may be staggered, so that tooth tip meets tooth trough. The latter alignment is the unique defining characteristic of a Wuest type herringbone gear, named after its inventor.
With the older method of fabrication, herringbone gears had a central channel separating the two oppositely-angled courses of teeth. This was necessary to permit the shaving tool to run out of the groove. The development of the Sykes gear shaper
Gear shaper
A gear shaper is a machine tool for cutting the teeth of internal or external gears. The name shaper relates to the fact that the cutter engages the part on the forward stroke and pulls away from the part on the return stroke, just like the clapper box on a planer shaper.The cutting tool is also...
made it possible to have continuous teeth, with no central gap. After the W.E. Sykes and Farrel Gear Machine companies dissolved in 1983-84 there are no current production machines that have this ability. It is standard industry practice to obtain an older machine and rebuild it if necessary to create this unique type of gear. A disadvantage of the herringbone gear is that it cannot be cut by simple gear hobbing machines, as the cutter would run into the other half of the gear. Solutions to this have included assembling small gears by stacking two helical gears together, cutting the gears with a central groove to provide clearance, and (particularly in the early days) by casting the gears to an accurate pattern and without further machining.
The logo of the car maker Citroën
Citroën
Citroën is a major French automobile manufacturer, part of the PSA Peugeot Citroën group.Founded in 1919 by French industrialist André-Gustave Citroën , Citroën was the first mass-production car company outside the USA and pioneered the modern concept of creating a sales and services network that...
is a graphic representation of a herringbone gear, it comes from André Citroën
André Citroën
André-Gustave Citroën was a French industrialist. He is remembered chiefly for the make of car named after him, but also for his application of double helical gears.- Life and career :...
's early involvement in the manufacture of these gears.
External links
- http://www.intechpower.com/Helical_and_Herringbone_Gears.html Picture showing helical and herringbone gears.
- http://productsearch.machinedesign.com/research/Mechanical_Components/Gears/Helical_Gears_Metric About herringbone gears.