AGMA 09FTM05-2009 pdf download.AGMA Technical Paper Hypoloid TM Gears with Small Shaft Angles and Zero to Large Offsets By Dr. H.J. Stadtfeld, The Gleason Works.
The basics of hypoloids
The generating principle is applied between the driving pinion and the driven gear. Although in most cases, pinion and gear might have the same number of teeth, the gear is used as a generating gear.
The new method even goes one step further and uses a non- generated gear with straight or curved tooth profile as generating gear for the pinion. In bevel and hypoid gears the non-generated principle is generally only used in cases when the ring gear pitch cone angle is 68 and higher. The Hypoloid method derives, in a first step, bevel gear machine basic settings for a non-generated gear member. Those settings are used to derive, in a second step, the basic settings for a bevel gear generator in order to manufacture the pinion. The cutter head for the pinion cutting (positioned by the basic settings and rotated around the cradle axis) represents one tooth of the non-generated gear member on which the pinion rolls during the generating roll process.
The principle of applying a non-generated gear member in order to generate the mating pinion is the only technique that delivers a precise conjugate relationship between pinion and gear, even if the axes of the two members are not in one plane. A conjugate basic geometry also requires the pitch cone to be parallel to the root cone. It has been observed that in case of low shaft angle spiral bevel gear sets, the tooth depth was calculated to be taller at the toe (reverse tooth taper) in order to fulfill the requirements of comp’eting (matching tooth thickness and opposite member slot width). One element of the Hypoloid geometry is a parallel depth tooth design, which will lead to more optimal tooth proportions than a reverse taper and also fulfill the requirement of parallelism between pitch line and root line. If the axes of the two members are in two parallel planes, the distance between the planes is defined as offset. In the case of conical pitch elements of the two members, this offset is commonly called hypoid offset.
One member is defined as a pinion (which is the generated member) and one member is defined as a gear (which is the non-generated member). In spite of the traditional definition, Hypoloid gears and pinions can have a similar number of teeth. It is even possible that the pinion has a higher number of teeth than the gear.
The conjugacy between the two members is only the basis for the generating principle. In order to make the gearset insensitive to tolerances in manufacturing and assembly, a located contact is achieved using flank surface crowning in the direction of the tooth profile, the lead and the path of contact.
If the non-generating process of the gear member is performed with straight cutting blades, then the generation of a pinion tooth will cause additional profile curvature versus an involute (oi’ more precisely defined as spherical involute or octoid). The additional pinion profile curvature can cause undercut in the pinion root area and a pointed topland. To reduce the additional profile curvature in the generated pinion, it is possible to manufacture the non-generated gear teeth with curved blades. If the gear cutter blades are foi-med like the involute of a similar generated gear, then the pinion tooth profiles will be regular involutes without additional profile curvature, without additional undercut in the root area and with no pointed topland versus a standard profile. It is also possible to approximate the involute function of the gear blade profile with circular or parabolic shape functions. This will achieve a similar effect and reduce the complexity of blade grinding or grinding wñeel dressing kinematics.AGMA 09FTM05 pdf download.