How to Calculate Thrust Load in Helical Gear
Helical gears are spur gears that contain their teeth set at an angle with regards to the axial centerline from the shaft supporting the apparatus, instead of parallel for it. One can use them for most high-speed automotive and machine applications where quiet operation and high loads are key factors. Helical gears have higher sideways thrust loads (axial loads) and slightly lower efficiency than straight spur gears, however, that makes their integrations more expensive to develop and operate. Calculating thrust loads for helical gears is therefore necessary to their proper design and implementation.
Transmissions use Helical gears since they are quiet.
Define the helical gear application. In cases like this, a reduction gear set employing helical gears is employed in a luxury inboard boat drive due to its smoothness and quiet operation. Engine torque at cruising speed is 360-foot-pounds. In the event the pitch diameter in the right-handed 22-tooth driving gear attached to the spinning engine shaft is 4 inches and also the diameter on the 44-tooth driven gear coupled to the propeller shaft is 8 inches and their helical angle, B, is 18 degrees, you are able to calculate the axial thrust developed by the driven helical gear as you move the boat is cruising.
Bevel gears in comparison to helical gears, change motion direction.
Consult a helical gear right-hand, left-hand gear sense diagram to get the direction in which the thrust will be directed and also a sense for your numbers you will be calculating. In cases like this, (all looking in the rear with the boat), the engine is rotating counter-clockwise, the propeller shaft is clockwise, the driving gear is helical right-hand, as well as the driven gear is helical left. Therefore, the driven helical gear will impart its thrust for the front in the gear case.
Calculate the instantaneous torque used on the propeller shaft. Because smaller 22-tooth gear is driving the greater 44-tooth gear, torque is doubled and speed is halved about the propeller shaft. Therefore, the driving torque placed on the propeller shaft is 360-foot-pounds x 2 = 720-foot-pounds.
Calculate the instantaneous tangential gear force Kt imparted for the teeth within the driven gear. The radius on the driven gear is 8 inches/2 = 4 inches. However, the torque transmitted is 720-foot-pounds. Therefore the torque has to be multiplied by 1 foot(12 inches)/4 inches = 3 x 720-foot-pounds = 2160-pounds of tangential force resistant to the gear at the point where its pitch circumference intersects the helical gear mesh.
Calculate the axial thrust within the driven helical gear. The Helical gears thrust equation is Ka (axial force) = Kt (tangential force) x tangent of angle B = 2160-pounds x 0.3249 (tangent worth of 18-degrees) = 701.82-pounds, directed toward the leading with the gear box. This might even be the axial thrust imparted on the smaller driving gear because their respective Kt values are indifferent, however the direction of the force for that smaller gear would be in the other way, toward a corner on the boat plus the common gearbox.