1、02FTM10Comparison in Rating Trends inAGMA versus ISOby: O.A. LaBath and D. Richter,Gear Consulting Services of Cincinnati, LLCTECHNICAL PAPERAmerican Gear Manufacturers AssociationComparison in Rating Trends in AGMA versus ISOO.A. LaBath and D. Richter, Gear Consulting Services of Cincinnati, LLCThe
2、statementsandopinionscontainedhereinarethoseoftheauthorandshouldnotbeconstruedasanofficialactionoropinion of the American Gear Manufacturers Association.AbstractIn the early 1980s, authors from The Cincinnati Gear Company presented several technical papers comparing the gearratingsfrom ISOand AGMA.
3、Thesecomparisonsshowed someinteresting and diversedifferences in the trendswhenthegeargeometrywaschangedslightly. Thesechangesincludedaddendummodificationcoefficients,helixangles,etc.There were also some interesting differences when the hardness and hardening methods were changed.These earlier paper
4、s used computer programs developed at The Cincinnati Gear Company to make both the ISO andAGMA ratings. Today, rating programs developed by an AGMA committee are available. The intent for this paper isto use these programs.Copyright 2002American Gear Manufacturers Association1500 King Street, Suite
5、201Alexandria, Virginia, 22314October, 2002ISBN: 1-55589-810-61Comparison of Rating Trends in AGMA Versus ISO Octave A. LaBath, PE and Dennis Richter Gear Consulting Services of Cincinnati, LLC INTRODUCTION: Many people have made comparisons of the differences in ratings between AGMA rating methods
6、and ISO rating methods. In 1977, G. Castellani 1 was the first to point out that there was a difference in the rating trend on spur gears when you change from standard gears to gears with a profile shift. In an ASME paper 2 presented in 1980 by Imwalle, LaBath, and Hutchenson, the comparisons of AGM
7、A and ISO ratings for 54 different gear sets were studied. In some cases large differences were calculated. In an AGMA paper 3 presented in 1981, LaBath made a comparison of the change in calculated stresses for three sample gear sets as a function of the profile shift and one sample as a function o
8、f the helix angle. The above study on the difference in trends for corrected gears and different helix angles was included in another AGMA paper 4 also presented in 1981, by Imwalle and LaBath along with a study on 156 gear sets. In the latter two papers, Imwalle and LaBath showed that with a positi
9、ve profile shift, the strength rating increases in AGMA and ISO but with different magnitudes. With a negative profile shift, the AGMA strength rating decreases and depending on the gear geometry, the ISO strength rating can go down or sometimes remain almost constant. The durability ratings also ha
10、d different trends for AGMA and ISO. The comparisons in the three papers by Imwalle, LaBath, and Hutchenson were based on computer programs written at The Cincinnati Gear Company for the then current AGMA rating standards and the draft ISO standards. The computer programs were based on the interpret
11、ation of the various standards by the engineers at Cincinnati Gear. In a 1989 AGMA paper 5, Dr. Hosel also reported that the rating trends were different for AGMA and DIN (ISO) with respect to the effect of profile shift on the ratings. In a 2002 paper prepared for NREL 6, Robert Errichello made a c
12、omparison of the different rating trends for AGMA and ISO. The durability rating trend for AGMA and ISO with respect to profile shift was almost the same for a spur gear sample. The strength rating trend was significantly different for the spur gear example. Mr. Errichello showed that the trends for
13、 both the strength rating and the durability rating were different for a helical gear example. Bob also showed that there was a difference in trends from AGMA and ISO for variations in the pressure angle. The comparisons made by Mr. Errichello were based on calculations made for AGMA by his GEARTECH
14、 AGMA218 program package and for ISO by the ISO 6336 Gear Rating Program copyrighted by AGMA in 1997. Calculation Method The comparisons made in this paper will be based on calculations made using the AGMA copyrighted ISO 6336 program and the newly developed AGMA program for calculations per ANSI/AG
15、MA 2001. These two programs are being released as Gear Rating Suite by AGMA. Using these two programs to do the rating comparisons, the results are independent of any one individuals opinion or interpretation of either standard. By using these programs, the input data for the gear geometry is the sa
16、me for both the AGMA and the ISO ratings. This allows for a consistent trend analysis by only changing one gear geometry parameter while holding all of the other gear geometry items constant within the program. The focus of this paper is to show the trends of the two rating systems by varying specif
17、ic geometry parameters one at a time. This paper is not trying to establish a rating constant between the two rating standards and should not be used as such. 2Examples similar to the three examples from the 1981 AGMA papers will be re-examined to determine the rating trends with respect to changes
18、in the profile shift. An example similar to the fourth example from the 1981 papers will also be re-examined to determine the rating trends with respect to changes in the helix angle. Two examples will be added to investigate the differences in rating trends with respect to pressure angle for a spur
19、 gear set and a helical gear set. We will rate the gears as carburized and hardened gearing ground to AGMA Class Q11. This is approximately ISO Class 6. We will assume that the material is per AGMA Grade 2 and ISO MQ. We will use the upper life factor curves and rate the gearing for a life of 10,000
20、 hours. The pinion speed will be set at 1750 rpm. An input power of 250 hp (186.3 kW) is being used and the programs are being used to calculate the factors of safety. In each example, the first calculated factor of safety becomes the reference factor of safety. The other calculated factors of safet
21、y are then divided by the reference factor of safety to get the Factor of Safety Trend value. In the tables, we are calling the Factor of Safety Trend FST. This is repeated for each rating item, pinion bending, gear bending, pinion durability, and gear durability. The Factor of Safety Trend is calcu
22、lated independently for AGMA and ISO. The Factor of Safety Trend value is then plotted versus the factor being varied for each example. How the Rating Programs Were Run The tooling was specified as not having protuberance. The tooling tip was specified to be a full root radius or as large as the geo
23、metry would allow. Since the ISO ratings are made with tooth thicknesses that do not include backlash, the AGMA ratings were also made with zero backlash. No grind stock was specified. The surface finish was specified as 32 RMS for both the flank and the root fillet. The leads were specified as havi
24、ng an ideal crown/correction with favorable tooth alignment. The gears were specified as commercial. The gear was specified as being a solid blank design. The bearing span was specified as being two times the face width. The gearing was centered in the bearing span. The ISO load distribution factor,
25、 KHbe, was calculated per method C1. The AGMA gear quality was specified as 11. The ISO quality was specified as class 8 for the pinion and class 7 for the gear. The ISO dynamic factor was specified per method B. The reliability was specified as 99%. The stresses were for industrial application, the
26、 upper curve. A 1.0 application factor was used. In AGMA, the strength ratings were calculated for the load applied at the HPSTC for the spur gear meshes. For ISO, a viscosity of 220 was specified. Again, the absolute ratings are not relevant to this study. The ratings calculated are consistent with
27、in the examples used and the trend differences are real. EXAMPLE #1 SPUR GEARING WITH VARYING PROFILE SHIFT COEFFICIENTS This example is a spur gear set operating on the standard center distance. The gear geometry is as follows: 21 teeth on the pinion 84 teeth on the gear 5 module (5.08 normal diame
28、tral pitch) 20 degree pressure angle 100 mm (3.939 inch) face width Standard hob proportions are being used Center Distance = 262.5 mm (10.3346) For this example, we will rate the gear set as a standard gear set and then rate it for increasing profile shifts or addendum modification coefficients on
29、the pinion. The profile shift coefficient is as it is defined in the MAAG Handbook 7. Since the center distance is being maintained at the standard center distance, the rack shift coefficient for the gear has the same value as the rack shift coefficient for the pinion but is positive on the pinion a
30、nd negative on the gear. The factors of safety for the various rack shift coefficients are given in Table 1. Table 1 and all of the other tables are presented at the end of this paper. 3This information has been normalized around the factors of safety for standard gearing and is plotted in Figures 1
31、-1, 1-2, 1-3, and 1-4. Figure 1-1 Example #1 Pinion Bending0.91.11.31.50 0.25 0.5 0.75Addendum ModificationFactor of SafetyTrendAGMAISOAs you can see, for this spur gear, both AGMA and ISO give an increased factor of safety for bending stress on the pinion when the addendum modification coefficient
32、is increased. This is what would be expected since the tooth thickness increases as the addendum coefficient is increased. As the value of the positive addendum modification is increased, AGMA gives more of an increase in the factor of safety than does ISO. Figure 1-2 Example #1 Gear Bending0.60.811
33、.20 0.25 0.5 0.75Negative Addendum Coefficient Factor of Safety Trend AGMAISOFor this plot, the addendum modification coefficient is negative. On this spur gear, AGMA gives a reduction in the factor of safety for bending when there is a negative addendum modification coefficient. As the value of the
34、 negative addendum modification coefficient is increased, AGMA gives a corresponding higher reduction in the factors of safety. This is what would be expected since the tooth thickness is reduced as the amount of the negative addendum modification is increased. In ISO, for this spur gear, the factor
35、s of safety for bending is almost independent of the increasing negative addendum modification coefficient and the decreasing tooth thickness. It is the goal of this paper to present the differences in the trends not to explain the differences. For this reason, there will be no discussion as to why
36、the AGMA and ISO results are so different. Figure 1-3 Example #1 Pinion Durability0.911.11.20 0.25 0.5 0.75Addendum CoefficientFactor of SafetyTrendAGMAISOWhen there is a positive addendum modification coefficient, both AGMA and ISO calculate a higher factor of safety for durability on this spur pin
37、ion. As the value of the positive addendum coefficient is increased, the factor of safety calculated increases for both AGMA and ISO. With an almost extreme value of positive addendum modification coefficient, x=.75, AGMA gives a slightly higher increase than ISO does. Figure 1-4 Example #1 Gear Dur
38、ability0.90.9511.051.11.151.20 0.25 0.5 0.75Negative Addendum CoefficientsFactor ofSafetyTrendAGMAISOEven though there is a negative addendum modification on the gear, both AGMA and ISO give an increase in the factors of safety for durability on this spur gear. The increase in the factor of safety i
39、s increasing with the increasing value of negative addendum modification coefficient. The increases in the factors of safety are higher in AGMA than they are in ISO. EXAMPLE #2 HELICAL GEARING WITH VARYING RACK SHIFT COEFFICIENTS This example is a helical gear set operating on the standard center di
40、stance. The gear geometry is the same as that used in Example #1. The only difference is the helix angle. Due to the helix angle, the standard center distance is a little larger than 4that used with the spur gearing in Example 1. Center Distance = 271.76 mm (10.6992). Again, we will rate the gear se
41、t as a standard gear set and then rate it for increasing profile shift coefficients on the pinion and decreasing negative profile shifts on the gear. The factors of safety for the various profile shift coefficients are given in Table 2. This information has been normalized around the factors of safe
42、ty for standard gearing and is plotted in Figures 2-1, 2-2, 2-3, and 2-4. Figure 2-1 Example #2 Pinion Bending 0.90.9511.051.11.151.20 0.25 0.5 0.75Addendum CoefficientFactorof SafetyTrendAGMAISOFor this helical pinion, both AGMA and ISO give an increased factor of safety for bending stress on the p
43、inion when the addendum modification coefficient is increased. Similar to the spur pinion example, as the value of the positive addendum modification is increased, AGMA gives more of an increase in the factor of safety than does ISO. Figure 2-2 Example #2 Gear Bending0.70.80.910 0.25 0.5 0.75Negativ
44、e Addendum CoefficientFactorofSafetyTrendAGMAISOOn the gear, the addendum modification coefficient is negative. On this helical gear, both AGMA and ISO give a reduction in the factor of safety for bending when there is a negative addendum modification coefficient. As the value of the negative addend
45、um modification coefficient is increased, both AGMA and ISO give a corresponding higher reduction in the factors of safety. The reduction in the factors of safety for bending by ISO is less than that from AGMA. Figure 2-3 Example #2 Pinion Durability 0.90.920.940.960.9811.021.041.060 0.25 0.5 0.75Ad
46、dendum CoefficientFactor ofSafetyTrendAGMAISOWhen there is a positive addendum modification coefficient on the pinion, AGMA calculates a higher factor of safety for durability on this helical pinion. As the value of the positive addendum coefficient is increased, the factor of safety calculated incr
47、eases for AGMA. Here, ISO is calculating a reduction in the factor of safety for durability on this helical pinion. As the addendum modification coefficient is increased, the ISO calculated factor of safety actually reduces. Even for x=.75, the differences in the factors of safety are less than 5% f
48、or both rating systems compared to a standard pinion. Figure 2-4 Example #2 Gear Durability0.90.920.940.960.9811.021.041.060 0.25 0.5 0.75Negative Addendum CoefficientFactor ofSafetyTrendAGMAISOSimilar to the spur gear example, even though there is a negative addendum modification on the gear, AGMA
49、gives an increase in the factors of safety for durability on this helical gear. The increase in the factor of safety is increasing with an increasing value of the negative addendum modification coefficient. In ISO, there is a decrease in the factor of safety for this helical gear when there is a negative addendum modification coefficient. As the value of the negative addendum coefficient is increased, there is a corresponding decrease in the factor of safety. Again, the differences are less than 5% compared to a standard gear. EXAMPLE #3 SPUR GEARING WITH VAR
