Hypoid Gears

Hypoid Gears are quite similar to the bevel gears. However they essentially operate on non-intersecting axes. Design wise Hypoid Gears are relatively novel and specialised. They are manufactured using the sophisticated "Gleason" machine tools. The spiral tooth of Hypoid Gears are oblique and curved. The axes can be at right angles or otherwise. Hypoid gears generally have pressure angles that is in the range of 19 and 22 degrees. Tooth engagement in Hypoid Gear is highlighted by adding a slippage in the direction of the tooth. This makes the Hypoid gears transmit rotation more smoothly and without noise as compared to spiral bevel gears.

Hypoid gears can be of the type anti-backlash, that means they have an inbuilt mechanism that can control backlash in the gear mesh. The following table gives the AGMA recommended Backlash range for Hypoid Gears.

A few other important specifications to be considered in Hypoid gears are the following:

Application of Hypoid Gears
Featured here is a typical application of Hypoid Gears. The model that is featured here is made of superior quality, heat treated hypoid steel gears that are subsequently heat treated. Two reasons why it is better than worm drive gears.

 

Breaking New Grounds in Hypoid Gear Technology: High Ratio Hypoid Gears A latest offering in the exciting world of Hypoid Gears is the one that comes with off-centre pinions in between a non-intersecting shaft. A characteristic feature of this particular type of gear is its very special capability to transmit higher loads. The new range is stated to have produced an exceptional speed reduction. Which is around 200:1 that too in a single pass. The component cost has been cut down sharply due to a compact gearing body. This has effectively replaced the numerous stages of reduction gears. In comparison to worm gears, the new novel design displays less sliding contact. This translates directly into higher efficiency.

 

Advantages of Hypoid Gears

• An unique single-stage design which eliminates backlash from the second set of meshing gears.
• Precise machining and assembly alignment makes it possible to have backlash =2 arcminutes.
• Greater tooth contact area means more load carrying capacity.

Comparison between Spiral Bevel Gears, Worm Gears and Hypoid Gears
As the image shows the conventional spiral bevel gearing, has essentially a pure rolling meshing action which is mechanically very efficient. But the drawback lies in its small total tooth contact area, resulting in a low torque throughput capacity. Not more than a 6:1 reduction ratio is possible in Single-stage spiral bevel gearing. However it may be possible to get higher ratios with the aid of multiple-stage configurations, but this comes with the problems of lower mechanical efficiency, increased backlash, more consumption of space and weight.

Next is the case of a conventional worm gearing, whose meshing position is shown at the top of the image. It has a considerably higher total tooth contact area. Though it offers a high torque throughput and a high ratio reduction, but in terms mechanical efficiency it fares poorly. This is due to the friction generated by its sliding action. Worm gearing is also affected by wear that demands regular adjustments for maintaining accuracy.

Lastly coming to the case of Hypoid Gears, it offers a rolling action along with a very small component of sliding action. Compared to bevel gearing, it shows a greater tooth contact area. As a result its load-carrying capability is more. In a single stage a 15:1 gear ratio is not impossible. Efficiencies can also be between 93% and 96%. And all these comes with a low backlash in the gear box.

 

Do you know? Hypoid gears are typiclly used for lowering the height of a driveshaft which helps to effectively lower the floor of a vehicle.

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