Planetary gear systems offer desired speed and torque variation with a compact and lighter construction than traditional gear trains. Transmission losses are one of the main concerns. Modification of gear teeth geometry is one of the remedial actions to reduce friction

Fatourehchi, Ehsan

King, Paul

Mohammadpour, Mahdi

Rahnejat, Homer

Trimmer, G

Womersley, B

Ehsan Fatourehchi (1257477)

Mahdi Mohammadpour (7204604)

Paul King (1247412)

Homer Rahnejat (1247550)

G. Trimmer (7206458)

B. Womersley (7206461)

Loughborough University Institutional Repository

TriboUK 2016 University of Leeds, April 14 – 15th, 2016   Effects of Gear Modification and Surface Finish on Planetary Gear Systems Efficiency Fatourehchi E*1, Mohammadpour M1, King P1, Rahnejat H1, Trimmer G2, Womersley B2 1 Wolfson School of Mechanical Engineering, Loughborough University, LE113TU 2 JCB Transmission, Wrexham Industrial Estate, Wrexham, UK *Corresponding author: E.Fatourehchi@lboro.ac.uk 1. Introduction Planetary gear systems offer desired speed and torque variation with a compact and lighter construction than traditional gear trains. Transmission losses are one of the main concerns. Modification of gear teeth geometry is one of the remedial actions to reduce friction. Ideal spur gears with line contact are very sensitive to misalignment and manufacturing errors which cause the edge loading contact of gear drive and increase gear noise. The simplest way to avoid the edge loading contact is to localize the mesh contact by crowning gear tooth surfaces. Several investigators such as; Seol and Kim [1] and Simon [2] have investigated improvements in the meshing contact stress distribution for misaligned spur gears through crowning. Additionally, planetary gear systems for off-highway applications are subject to high contact pressures up to 1.2 GPa, which can result in asperity interactions within the mating teeth pair contacts. Therefore, better surface finish helps to reduce boundary friction. This study aims to ascertain the overall system effects of different extent of crowning of planetary spur gears with varying surface roughness. 2. Methodology The devised methodology enables prediction of frictional losses. The method integrates TCA (Tooth Contact Analysis) to determine the instantaneous contact geometry, kinematics of contact and load distribution, which are used in an analytical EHL model for prediction of meshing power losses.  The lubricant film thickness under the instantaneous operating conditions is obtained using Chittenden et al. [3] extrapolated lubricant film thickness formula. Predicted film thickness is then used in Evans and Johnson [4] approach to analyse viscous friction in EHL contacts. With the high loads experienced by gears in off-highway planetary spur gear systems, the lubricant operates in the Eyring traction regime. Consequently, the coefficient of friction is calculated using [4]:     where,  The generated friction due to viscous shear of the lubricant film is expressed as: 𝑓𝑓𝑣𝑣 = 𝜇𝜇𝜇𝜇 Thin lubricant films in the meshing contacts of loaded gear teeth pairs in off-highway applications are comparable to the height of surface asperities. Consequently, asperity interactions, and therefore boundary friction is to be expected. Greenwood and Tripp [5] method is used to obtain boundary friction within the contact. Finally, the instantaneous power loss is determined by taking into account the calculated viscous and boundary friction contributions as: 𝑃𝑃𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 = (𝑓𝑓𝑣𝑣 + 𝑓𝑓𝑏𝑏)𝑈𝑈𝑙𝑙 where, 𝑈𝑈𝑠𝑠 is the instantaneous contact sliding velocity determined through TCA.  3. Results The effect of gear crowning with different surface roughness on power loss is investigated. Figure 1 shows the predicted instantaneous total power loss during a typical meshing cycle for the sun-planet contact. Considering two identical planetary gear hubs with three planet gears, Table 1 depicts the average total power loss for different values of surface roughness.    Figure 1: Total power loss, Sun-Planet Contact Table 1: Total power loss of two planetary gear hub Surface Roughness (μm) 0.4 1.2 2 2.8 3.6 Average Total Power Loss [W] 267.8 272.3 273.2 273.6 273.9 % increase in total power loss compare to 0.4 μm roughness - 1.66 2.02 2.17 2.26 4. Acknowledgement  The authors would like to express their gratitude to JCB transmission and Innovate UK for their support of this research. 5. References [1] Seol, I. H., and Kim, D. H., “The Kinematics and Dynamic Analysis of Crowned Spur Gear Drive,” Comput. Methods Appl. Mech. Eng., 167:109–118, 1998. [2] Simon, V., ‘‘Optimal Tooth Modifications for Spur and Helical Gears,’’ ASME Journal of Mech. Trans. Auto. Design, 111:611–615, 1989. [3] Chittenden, R. J. Dowson, D., Dunn, J. F. and Taylor, C. M., “A theoretical analysis of the isothermal elastohydrodynamic lubrication of concentrated contacts. II. General Case, with lubricant entrainment along either principal axis of the Hertzian contact ellipse or at some intermediate angle,” Proc. Roy. Soc., Ser. A, 397:271-294, 1985.   [4] Evans C.R. and Johnson K.L., “Regimes of traction in elastohydrodynamic lubrication,” Proc Instn Mech Engrs, 200(C5): 313–324, 1986. [5] Greenwood J.A., and Tripp J.H., “The contact of two nominally flat rough surfaces,” Proc Instn Mech Engrs 185: 625–633, 1970. 

English

Effects of gear modification and surface finish on planetary gear systems efficiency

CLoK

This item was submitted to Loughborough's Research Repository by the author. Items in Figshare are protected by copyright, with all rights reserved, unless otherwise indicated.Effects of gear modification and surface finish on planetary gear systemsefficiencyPLEASE CITE THE PUBLISHED VERSIONhttps://tribouk2016.org.uk/PUBLISHERTriboUKVERSIONVoR (Version of Record)PUBLISHER STATEMENTThis work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at:https://creativecommons.org/licenses/by-nc-nd/4.0/LICENCECC BY-NC-ND 4.0REPOSITORY RECORDFatourehchi, Ehsan, Mahdi Mohammadpour, P.D. King, Homer Rahnejat, G. Trimmer, and B. Womersley.2019. “Effects of Gear Modification and Surface Finish on Planetary Gear Systems Efficiency”. figshare.https://hdl.handle.net/2134/21583.TriboUK 2016 University of Leeds, April 14 – 15th, 2016   Effects of Gear Modification and Surface Finish on Planetary Gear Systems Efficiency Fatourehchi E*1, Mohammadpour M1, King P1, Rahnejat H1, Trimmer G2, Womersley B2 1 Wolfson School of Mechanical Engineering, Loughborough University, LE113TU 2 JCB Transmission, Wrexham Industrial Estate, Wrexham, UK *Corresponding author: E.Fatourehchi@lboro.ac.uk 1. Introduction Planetary gear systems offer desired speed and torque variation with a compact and lighter construction than traditional gear trains. Transmission losses are one of the main concerns. Modification of gear teeth geometry is one of the remedial actions to reduce friction. Ideal spur gears with line contact are very sensitive to misalignment and manufacturing errors which cause the edge loading contact of gear drive and increase gear noise. The simplest way to avoid the edge loading contact is to localize the mesh contact by crowning gear tooth surfaces. Several investigators such as; Seol and Kim [1] and Simon [2] have investigated improvements in the meshing contact stress distribution for misaligned spur gears through crowning. Additionally, planetary gear systems for off-highway applications are subject to high contact pressures up to 1.2 GPa, which can result in asperity interactions within the mating teeth pair contacts. Therefore, better surface finish helps to reduce boundary friction. This study aims to ascertain the overall system effects of different extent of crowning of planetary spur gears with varying surface roughness. 2. Methodology The devised methodology enables prediction of frictional losses. The method integrates TCA (Tooth Contact Analysis) to determine the instantaneous contact geometry, kinematics of contact and load distribution, which are used in an analytical EHL model for prediction of meshing power losses.  The lubricant film thickness under the instantaneous operating conditions is obtained using Chittenden et al. [3] extrapolated lubricant film thickness formula. Predicted film thickness is then used in Evans and Johnson [4] approach to analyse viscous friction in EHL contacts. With the high loads experienced by gears in off-highway planetary spur gear systems, the lubricant operates in the Eyring traction regime. Consequently, the coefficient of friction is calculated using [4]:     where,  The generated friction due to viscous shear of the lubricant film is expressed as: 𝑓𝑓𝑣𝑣 = 𝜇𝜇𝜇𝜇 Thin lubricant films in the meshing contacts of loaded gear teeth pairs in off-highway applications are comparable to the height of surface asperities. Consequently, asperity interactions, and therefore boundary friction is to be expected. Greenwood and Tripp [5] method is used to obtain boundary friction within the contact. Finally, the instantaneous power loss is determined by taking into account the calculated viscous and boundary friction contributions as: 𝑃𝑃𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 = (𝑓𝑓𝑣𝑣 + 𝑓𝑓𝑏𝑏)𝑈𝑈𝑙𝑙 where, 𝑈𝑈𝑠𝑠 is the instantaneous contact sliding velocity determined through TCA.  3. Results The effect of gear crowning with different surface roughness on power loss is investigated. Figure 1 shows the predicted instantaneous total power loss during a typical meshing cycle for the sun-planet contact. Considering two identical planetary gear hubs with three planet gears, Table 1 depicts the average total power loss for different values of surface roughness.    Figure 1: Total power loss, Sun-Planet Contact Table 1: Total power loss of two planetary gear hub Surface Roughness (μm) 0.4 1.2 2 2.8 3.6 Average Total Power Loss [W] 267.8 272.3 273.2 273.6 273.9 % increase in total power loss compare to 0.4 μm roughness - 1.66 2.02 2.17 2.26 4. Acknowledgement  The authors would like to express their gratitude to JCB transmission and Innovate UK for their support of this research. 5. References [1] Seol, I. H., and Kim, D. H., “The Kinematics and Dynamic Analysis of Crowned Spur Gear Drive,” Comput. Methods Appl. Mech. Eng., 167:109–118, 1998. [2] Simon, V., ‘‘Optimal Tooth Modifications for Spur and Helical Gears,’’ ASME Journal of Mech. Trans. Auto. Design, 111:611–615, 1989. [3] Chittenden, R. J. Dowson, D., Dunn, J. F. and Taylor, C. M., “A theoretical analysis of the isothermal elastohydrodynamic lubrication of concentrated contacts. II. General Case, with lubricant entrainment along either principal axis of the Hertzian contact ellipse or at some intermediate angle,” Proc. Roy. Soc., Ser. A, 397:271-294, 1985.   [4] Evans C.R. and Johnson K.L., “Regimes of traction in elastohydrodynamic lubrication,” Proc Instn Mech Engrs, 200(C5): 313–324, 1986. [5] Greenwood J.A., and Tripp J.H., “The contact of two nominally flat rough surfaces,” Proc Instn Mech Engrs 185: 625–633, 1970. 

Effects of Gear Modification and Surface Finish on Planetary Gear Systems Efficiency

http://clok.uclan.ac.uk/32163/1/32163%20Tribouk2016_Ehsan%20Fatourehchi_Loughborough%20University.pdf

Effects of Gear Modification and Surface Finish on Planetary Gear Systems Efficiency

Abstract

Similar works

Full text

Available Versions

Loughborough University Institutional Repository

CLoK