1、 STD-AGMA SbFTMS-ENGL L7Sb Ob87575 0004877 250 W 96IiTM5 Differential Crowning: A New Weapon Against Gear Noise and Dynamic Load by: Mark Wyeth and William S. Rouverol, Axicon Gear Company TECHNICAL PAPER - - STD-AGMA SbFTMS-ENGL L79b Ob87575 0004878 197 W Differential Crowning: A New Weapon Against
2、 Gear Noise and Dynamic Load Mark Wyeth and William S. Rouverol, Axicon Gear Company The statements and opinions contained herein are those of the author and should not be construeL as an official action or opinion of the American Gear Manufacturers Association. Abstract As the power density of gear
3、 sets increases, mesh deflections increase, and the variations in those deflections, which result primarily from mesh stiffness variation, become increasingly signifcant. This is because these variations translate directly into transmission error and provide the excitation that generates the periodi
4、c inertial load supplement called “the dynamic increment of load”. In addition to subtracting from the useful torque capacity, the dynamic increment is the main generator of gear noise. To minimize these undesirable effects, designers of power train gear pairs have traditionally specified various fo
5、rms of profile modification, the most common of which is tip and/or root relief. The problem with these conventional modificationsisthat they give only a limited reduction in transmission error at a particular roll angle and load (the “design load”) but produce increases in transmissi on error at ot
6、her roll angles and loads. A new system of modifications, however, has recently been devised that substantially eliminates mesh stiffness variations throughout the entire engagement angle regardless of what torque load is being transmitted. This new system of modifications is described and confirmat
7、ory test results are reported. By substantially eliminating gear noise and dynamic increment, the new modifications make it possible to replace costly helical gear sets with better performing spur sets in many applications. in addition, gear sets embodying these new modifications are significantly l
8、ess sensitive to profile manufacturing errors than gear sets having tip and/or root relief. Together, these features can lead to substantial reductions in cost without compromising performance. Copyright O 1996 American Gear Manufacturers Association 1500 King Street, Suite 201 Alexandria, Virginia,
9、 22314 October, 1996 ISBN: 1-55589-672-3 - STD-ALMA SbFTMS-ENGL LSSb Ob87575 OOOLi879 U23 a DIFFERENTIAL CROWNING: A NEW WEAPON AGAINST GEAR NOISE AND DYNAMIC LOAD William S. Rouverol General Partner Axicon Gear Company Berkeley, California INTRODUCTION There are two major disadvantages in the curre
10、nt method of m0-g power train gearing, both of which lead to significant increases in transmission error. Since transmission error generates a dynamic increment of load that not only suberacts fiom the useful torque capacity of a gear set but is also the primary source of gear noise excitation, anyt
11、hing that increases transmission error automatidy detracts from gear performance and indirectly increases power train costs. The two disadvantages inherent in the present system of specZying gear profile mdications are: (I) it is “load-specific“ and (2) it is higbiy sensitive to manufacturing inaccu
12、racy. LOADSPECIFIC MODIFICATIONS Most of the worlds gearing is called on to transmit a very wide range of loads. Vehicle propulsion gearing, for example, which coI1stiMes approximately three-fourths of the worlds gearing, is required to transmit torques fiom the peak allowable ail the way down to ze
13、ro and into reverse. Up to the present time all of this gearing that is called on to transmit major variations in torque has been given modifications that are “load-specific“, that is to say, modifications that are correct for one particular load but are either insuniCient or excessive for ail other
14、 loads. That such non-optimum modifications produce substantial increases in transmission error has been noted by the AGMA in its most widely used Standard: “Since elastic deflections are load dependent, gear tooth protile modifications can be designed to give a uniform velocity ratio only for one l
15、oad magnitude. Loads different fom the design load will give increased transmission error.“ (Ref. 1) The physical characteristics that cause conventional tip and/or root modifications to be “load-specific“ are expiained i11 Figs. 1 and 2. Fig. 1 shows tooth pair stiffness k plotted as a function of
16、contact psition along the path of contact (or as a function of the roll angle, since z varies as the product of the roll angle and the base radius). As the figure indicates, CUN e-f-c-g has its effective stifhess reduced over the relieved tip portion e-c, by the amount shown shaded. If the right amo
17、unt of tip and/or root relief is provided, stiffness ordinate j-f at the roll angle of point j is reduced to j-b, which is exactly half the stifless h-g at roii angle 4 eliminating, at least for the design load, the mesh sfiffness variation that generates the first harmonic of gear pair excitation.
18、(A symmetrical mesh stiffkess curve is shown in Fig. 1, in the interest of simplicity. When the gear ratio is greater than unity, the basic mesh stifkess curve is asymmetrical.) n d -9 1L k 1 h n J Roil Angle Figure 1: Effects of conventional profile modifications on a tooth pair stiffness curve at
19、the design load. -1- STD-AGMA SbFTMS-ENGL L77b II Ob87575 0004880 BY5 Why this system of gear tooth modincation runs into trouble at low loads is due to using an inherently non-hear method to adjust tooth stifiess. The profile modification that produced the ideal stifhess for the design load (ordina
20、te j-b in Fig. i) introduces a greatly reduced sti 5,341,699; and 5,485,761; and anaiogous foreign patent applications. 3. Hirt, M., “German and American Quaiity System of Spur, Helical and Bevel Gears: Influence of Gear Quaiity on Costs and Load Capacity“. ASME Paper 8O-C2/DET-18 (Ref. Figs. 1 and4). -4-
