Friction loss and surface durability of WN gears a comparison with Involute gears

This is a comparative study of Involute and WN gears. Two kinds of tooth profile were used in this issue. One is a nearly standard gear with involute tooth profile, the other is a Wildhaber-Novikov or circular-arc profile. WN gears are used to be transmitted motion and power between parallel shafts. It is known that teeth of WN gears theoretically contact at a point, in transverse section, but the contact point extends over a small ellipse due to elastic deformation under load. Abovementioned reason, the gears must have helical tooth form. However, the contact area is considerably greater than corresponding involute teeth, and thereby make possible to be greater surface durability. In addition, the sliding velocity is constant along tooth trace and comparatively lower than involute gears. Moreover, there are several disadvantages of the application. The contact stress between the tooth surfaces of WN gears is comparatively low. Furthermore, the sliding velocity on the tooth surfaces is lower than for other kinds of involute gears. For a long time, these gears are used for heavy loads in low speed. But only a few experimental results about their load carrying characteristics have been reported. The load carrying characteristics of these helical gears were investigated by means of power circulating test rig. The experiments concerning frictional loss were carried out quite separately from the experiments of limiting load for pitting. The running-in of test gears was carried out enough. After the running-in the running state of test gears became stable and there was no fluctuation of power loss. For measurement of friction loss, two torque-meters of magneto-striction type were installed. And then, the friction loss of the gears was measured by monitoring the input torque and output torque of gearing. In order to obtain the experimental results of the limiting load for pitting, the modified FZG test was chosen. This method is according to the DIN standard. Experiments concerning the friction loss and the limiting load for pitting were carried out and the results were summarized.