1、 Access to Additional Content for ISO/TR 22849 First edition, Dated: 04/15/2011 (Click here to view the publication) This Page is not part of the original publication This page has been added by IHS as a convenience to the user in order to provide access to additional content as authorized by the Co
2、pyright holder of this document Click the link(s) below to access the content and use normal procedures for downloading or opening the files. ISO/TR 22849 Files Information contained in the above is the property of the Copyright holder and all Notice of Disclaimer the most significant is Hertzian co
3、ntact (compressive) stresses between the two mating tooth surfaces and is proportional to the square root of the applied tooth load. The ability of bevel and hypoid gear teeth to withstand repeated surface contact under load without destructive pitting involves the resistance of the gear material to
4、 fatigue under contact stresses. The smaller gear is usually the limiting member of the pair because the teeth receive more stress cycles per unit time. In some cases, the smaller gear is made harder than its mate, to increase its surface durability so that the limiting capacity can exist in either
5、member. ISO/TR 22849:2011(E) 4 ISO 2011 All rights reserved3.2.4 Other forms of bevel gear tooth deterioration The rating standards are not applicable to other types of gear tooth deterioration such as micropitting, case crushing, wear, plastic yielding and welding. Information on scuffing can be fo
6、und in ISO/TR 13989-1. 3.3 Materials The quality of materials and methods of heat treatment required are governed by the application. Care should be taken to choose the proper material for each application to transmit the load and obtain the life desired. Heat treatment is usually needed to develop
7、the necessary hardness, strength and wear resistance. For information about materials and heat treatment, see ISO 6336-5. 3.4 Gear tolerances Bevel gears are manufactured to suit many engineering applications. In order to satisfy these needs properly, it is necessary to analyse the conditions under
8、which these gears should operate. Reasonable tolerances should then be established to ensure that the gears perform satisfactorily in the application. Tolerance values for unassembled bevel gears, hypoid gears and gear pairs are provided in ISO 17485. Additionally, information about bevel gear measu
9、rement methods is given in ISO/TR 10064-6. 3.5 Gear noise 3.5.1 General The gear noise can be produced by the vibration of the gear unit caused by the transmission error of the gear pair. The flank form deviations of the teeth, a misalignment between the gears, and the elastic deformation of the tee
10、th under load affect the transmission error. Table 1 shows typical values of transmission errors for different gear applications. Table 1 Typical values of transmission error Application Recommendation value rad Passenger car 30 Truck 20 to 50 Industrial 40 to 100 Aircraft 40 to 200 (80 average) ISO
11、/TR 22849:2011(E) ISO 2011 All rights reserved 53.5.2 Tooth flank form corrections The tooth flank form of bevel gears is corrected in order to prevent edge contact of tooth bearing during operation. Figure 1 a) shows the tooth flank form deviation of a spiral bevel gear after lapping. The amount of
12、 deviation between adjoining contour lines is 2 m. It turns out that a crowning of remarkable size occurs in face width direction. On the other hand, the amount of deviation in the profile direction is small. Figure 1 b) shows the pertaining tooth bearing and Figure 1 c) the waveform of the transmis
13、sion error. The peak-to-peak value of the transmission error is 24 rad. a) Tooth flank deviation b) Tooth bearing c) Transmission error Figure 1 Example of a gear pair finished by lapping process Figure 2 shows the effect of profile crowning and flank twist where the amount of lengthwise crowning is
14、 fixed at 20 m. In the case of 5 m profile crowning in Figure 2 a), the width of tooth bearing is wide, and the transmission error is 27 m. On the other hand, in the case of 20 m profile crowning in Figure 2 b), the width of tooth bearing is narrow, and the transmission error increases to 43 m. This
15、 means that excessive profile crowning should be avoided. However, in the case of Figure 2 c) with a flank twist correction of 80 m, the transmission error decreases to 24 rad. This shows the effectiveness of flank twist modifications if the profile crowning is enlarged. ISO/TR 22849:2011(E) 6 ISO 2
16、011 All rights reservedNOTE The transmission error is 27 rad. NOTE The transmission error is 43 rad. a) Profile crowning of 5 m b) Profile crowning of 20 m NOTE The transmission error is 24 rad. c) Profile crowning at 20 m and flank twist of 80 m Figure 2 Effect of profile crowning and flank twist o
17、n transmission error Lengthwise crowning of 20 m Since tooth flanks are subject to elastic deformations under load, this needs to be considered for flank form corrections. However, as the noise of a gear set in many cases becomes a problem under light load, the measure indicated above is rather effe
18、ctive. ISO/TR 22849:2011(E) ISO 2011 All rights reserved 73.5.3 Design contact ratio NOTE The transmission error is 24 rad. NOTE The transmission error is 52 rad. a) Number of teeth of 10/43 and contact ratio of 3:02 b) Number of teeth of 7/30 and contact ratio of 2:23 Figure 3 The effect of design
19、contact ratio on transmission error The design contact ratio is the angle of transmission of one pair of teeth divided by the angular pitch. It is favourable, therefore, to enlarge the design contact ratio of a gear set in order to reduce gear noise. To get a higher design contact ratio, it is effec
20、tive to increase the number of teeth, to enlarge the working tooth depth and to increase the spiral angle. However, if the number of teeth is increased, the mean normal module becomes smaller and reduces the load carrying capacity. Moreover, there is a risk that undercut can occur in the pinion root
21、 or the topland can become too small if the tooth depth is enlarged too much. Caution is required in those points. Figure 3 shows the effect of design contact ratio on the transmission error. In the case of smaller tooth numbers of 7/30, the contact ratio which is less than that of 10/43, the size o
22、f the tooth bearing increases, but the transmission error also increases from 24 rad to 52 rad, although the tooth flank deviations are the same. The actual contact ratio can change under load by deformation of the flanks and deflections of teeth and shafts. 3.5.4 Other noise consideration Where a l
23、arge misalignment is in the mountings of a gear pair or the misalignment produced by deflection under load is considerable, the tooth flanks can have edge contact and the transmission error can increase. Therefore, caution is advised to make the mountings of the gears accurate and the rigidity of the gearbox high.
