No abstract

Pitting and micropitting are the two main gear rolling contact fatigue modes. It is widely accepted that micropitting will lead to pitting; however, the relationship between pitting and micropitting life needs further investigation. In this work, micropitting and pitting tests were performed on an FZG back-to-back test rig using standard FZG PT-C and GF-C gears. The gear tooth profile change due to micropitting and pitting damage was measured in situ in the gearbox using a profilometer after each test. The gear surface roughness parameters were calculated from the measured tooth profile. A Gaussian low pass filter with cut off length [Formula: see text] mm was applied to the measured tooth profile to obtain the waviness. The calculated roughness parameters and the obtained tooth profile with waviness for each test were imported into the KISSsoft software to calculate the contact stress and specific film thickness at the corresponding load stage. Experimental results show that smooth gear surface can reduce or even avoid micropitting damage, but could lead to a reduction in pitting life.

No abstract

To increase the efficiency of a gearbox, research on gear mesh loss is of importance. Britton et al. concluded that the surface finishing method affects the gear mesh efficiency. The efficiency benefits of superfinishing a surface and reducing the surface roughness have been reported by Kahraman. A novel method for calculating the bearing loss torque was proposed by Tu et al. Andersson et al. found that the efficiency can vary between 2 and 5% during repeated efficiency tests due to variations in the assembly process. This work investigates how the honing surface finishing process and DIN 3962 quality class affect the gear mesh efficiency by performing tests in an FZG back-to-back test rig. Two materials, a powder metal and a wrought steel, were tested. All gears were finished using a honing process and sorted according the measured quality class. Powder metal gears of class 6, 7, 8, and !9 and wrought steel gears of class 6, 7, and !9 were tested. The efficiency were calculated from measuring the torque required to maintain a constant velocity of the FZG test rig. The results from the efficiency tests showed no significant difference in efficiency between the wrought steel and powder metal steel gears. In addition, no obvious correlation between the DIN 3962 quality class and the gear mesh efficiency could be found. When examining the wrought steel material it was found that the reproducibility of the efficiency was comparable to the assembly error of the test rig, despite the variation in quality class.

According to the GFKT-C/8.3/90 FZG gear micropitting test procedure, the average value of gear tooth profile deviation is used as the failure criterion. Typically, gear tooth profile deviation is measured using a gear measuring machine. In order to do that during the FZG gear test, the gears tested have to be disassembled from, and assembled to the test rig. This process is tedious, timeconsuming and is likely to add uncertainty to the testing results. An in situ gear tooth profile measurement method has been developed and applied in FZG gear micropitting tests. The tooth profile of the tested gear was measured in-situ in the gearbox before, during and after each load stage of the gear micropitting test. An algorithm was developed to fit the measured profile to its theoretical shape. Furthermore, a tooth profile change evaluation algorithm was developed for monitoring the evolution of the tooth profile during the duration of the test. The whole methodology was exemplified with a wrought gear test case run to pitting damage.