What does the 'n' curve in the Harris diagram for gears signify?

[k.udhay]

Hi,
I started reading about mesh stiffness and came across an interesting diagram called “Harris diagram” which represents the relationship between profile corrections and transmission error. Naturally, I ended up with few doubts, that I thought I could ask :

1. I am unable to understand the second curve ‘n’, which is observed for a small load. At pitch point region due to deflection, there is an offset of the line but still it is a horizontal line. As soon as the tip relief region comes (“changeover point” region), the curve starts sloping down. I am alright till this point. But after this point another small horizontal line exists till the second pair of teeth (with relief) contact. What causes this small horizontal line and what is this signifying?

2. The last line has a convex horizontal line in the “changeover point” region. Does that mean that there will be an interference between the driven and the driver teeth at the beginning of mesh? In other words, would the driver have been in a leading position and driven in lagging position with reference to the theoretical condition?

Thanks.

P.s. - The basics of this is explained in the book 'Gear Noise And Vibration' by J. Derek Smith starting from Page no. 19.

 

[Navin A S]

1. The small horizontal line signifies the amount of profile error after the changeover point before the second pair of teeth with relief contact. This is due to the profile shift that occurs as a result of the gear mesh stiffness. As the gear teeth are subjected to pressure and friction, they shift slightly out of their original position, resulting in a slight misalignment between the driver and driven teeth. This misalignment causes the gear mesh to become stiffer, which is represented by the horizontal line.2. Yes, the convex horizontal line in the “changeover point” region means that there will be an interference between the driven and the driver teeth at the beginning of mesh. The convex shape indicates that the driver has been in a leading position and driven in lagging position with reference to the theoretical condition.