Gear AT Shape Definition allows you to create a property file (*.hgp) that defines the topology of a bevel or hypoid gear (both macro and micro geometry). In current release you can define a tooth profile by processing of CAD data only. Figure 171 shows how to access the tools you need to define your bevel or hypoid gear geometry.

Tooth profiles are extracted from full gear geometry defined by CAD data. The tooth boundaries and number of segments over tooth lead direction are specified in the definition file ( *.hgd).

During Bevel/Hypoid Shape Definition process an intersecting solid is created, which is substracted from CAD geometry. This will create two new solids - rim and web. The rim is used to extract the tooth profiles and the web remains stored in the working directory (*.xmt_txt) and can be further used to create the FE structure to model the full flex gear as shown on Figure 237.

 

 

Depending on complexity of geometry and number of segments requested the shape definition process can take from several minutes up to 1 hour.

 

The Gear AT Shape Definition has following tabs to help you create a gear

 

The Gear AT Shape Definition has following tabs to help you edit a gear

 

 

 

Define layout of gear pair and preview gear assembly. Besides Pitch Apex Beyond Crossing Point parameters remaining entries have no impact on the Shape Definition processing of CAD geometry of the gears. Some of the fields are not editable and are provided for information only. Meaning of parameters and convention used is depicted on Figure 240 and Figure 241.

 

 

 

Note that Pitch Apex Beyond Crossing Point parameter is linked to the parameter in Assembly tab. Hand of Spiral radio button is linked between Gear 1 and Gear 2 tab and affects the direction of pinion offset (above or below centre) - see Figure 241. Dimensions entered in this tab and conventions used are explained in Figure 243.

 

 

 

 

Review basic geometrical parameters in the General tab (Figure 247). Since the tooth profiles have been extracted already and are stored in *.hgp file the values in fields are not editable.

 

The Mass card of the Shape Definition process allows you to define the mass of the gear based either on the Geometry and Material Type or by specific User Input (Figure 205). In the former case the mass, center of mass and inertia tensor is computed later on by the mesher based on FE mesh volume. In the latter case enter all required data in current model units. In either case, inertia data are written to the *.hgp file.

 

Gear tooth flank modifications are applied to compensate for manufacturing errors, deformation of the teeth due to load and also for shafts and gear housing deformation thus ensure a proper meshing to achieve more favorable load distribution and reduced transmission error. The ultimate goal is to reduce gear wear and vibrations induced by the gear pair operation, thus help to design durable gearbox fulfilling specified NVH parameters.

 

Gear AT supports following gear profile and lead modifications which are all superimposed over the tooth flank:

 

 

Barreling (profile crowning) is a convex shape added to the involute curve to prevent hard contact near the tip and root. Barreling is defined as a polynomial function of the dimensionless involute curve parameter u. Eccentric barreling can be used to apply different relief at root and tip form cone. Eccentricity factor corresponds to ratio of diameters rather than length of contact path.

 

Involute slope is used to compensate for tooth deflection differences between the two meshing gears and to compensate for system deflections that would otherwise result in hard contact near the root or the tip of one of the gears. It defines correction in pressure angle relative to root form cone. The positive correction removes material on tip as shown by Figure 252 for the left flank, while negative correction removes material on root.

Twist modification is a flank surface torsion along the lead line which is ;ocated in the middle of profile, see Figure 253. The twist is applied in correlation with involute slope, but always with opposite sign on tooth sides. The positive value means linear increase of torsion angle from negative side to positive side of flank, see Figure 253 and Figure 254.

Lead modifications are used to attain a low displacement sensitivity and to avoid strain peaks occurring due to displaced positions of the gear axis or spiral deviations of the flank. Types of lead modifications for bevel and hypoid gears supported by Gear AT include crowning and lead slope changes. The Figure 255 shows lead modifications card layout for the left flank.

 

Crowning is convex shape along the width of a tooth. It is used to maintain contact in the central region of the tooth flank width allowing for gear angular and axial misalignment. This type of tooth modification is preferably used on narrow gears. The amount of crowning should not be larger than necessary as otherwise it would reduce area of contact, thus lowering load capacity of a gear pair.

Crowning is applied in a perpendicular plane to the contour of the tooth. Crowning is defined as a polynomial function of a dimensionless parameter u (Figure 256). The distribution of the crowning across the flank width can be linear, quadratic, cubic or custom. The custom option allows direct definition of crowning function coefficients, thus allow the combination of distribution types previously mentioned, say linear with quadratic distribution.

The dimensionless parameter u follows from Equation  (24), the polynomial function is given in the Equation  (25):

 

The Equation  (26) gives the relation between the crowning drop and crowning radius R. In general, is very small compared to the width of the tooth; so Equation  (27) should be a valid approximation for a circular crowning:

Lead Slope defines correction of the helix angle (Figure 257), which is used to improve contact with mating gear teeth when system deflections would otherwise cause edge loading.

The positive sign of the lead slope modification yields the same sense of spiral angle change for both, left and right flank. The positive correction is depicted on Figure 257, while the negative is on Figure 258.

You can define bevel / hypoid gear manufacturing errors to be taken into account in the contact simulation. Enter Radius Error for every tooth to describe deviations from ideal pitch circle and enter Pitch Error for every tooth to describe deviations from angular pitch, see Figure 259.You can also enter amplitude and phase shift to generate harmonic distribution of error by cosine function or apply generator of random numbers to get random distribution from interval of <-amplitude , + amplitude>. Positive value of Radius Error results in larger tooth radius and positive Pitch Error rotates tooth in counter clock-wise direction according to the right hand rule.