A double helical gear incorporates two opposite orientated helical gears of the same helix angle together such that the two opposing thrust forces annihilates one another.
Double helical gears sometimes counteract or nullify the forces to overcome axial thrust. The total face is made into two equal halves, both with the same helix angle but with opposite hands (1,2). The axial thrusts are opposite one another, and the forces are contained in the gear and not transmitted to the bearing.
Therefore, high loading capability and steady transmission are advantaged. Due to their advantages, double helical gears have been widely used for power transmission in gas turbine, generators, prime mover, pump, fan, and compressor in marine ships and construction machine.
The large-sized double helical gears are usually generated using a special generator.