Abstract: A polishing nanofiber aggregate and a method for producing the same are provided that are capable of suppressing a decrease in polishing efficiency even using fine powder for precision polishing. A polishing nanofiber aggregate 1 is used by adsorbing a slurry prepared by mixing fine powder for precision polishing with a liquid. The polishing nanofiber aggregate 1 has an average fiber diameter d of 400 nm or more and 1000 nm or less and a porosity ? of 0.70 or more and 0.95 or less. The polishing nanofiber aggregate 1 is capable of reducing an interfiber distance e1 while securing the porosity ?. It is thus possible to suppress incorporation of abrasive particles having a small diameter between the fibers.

Abstract: In optimum number of teeth setting method for a helical gear pair and the helical gear pair manufactured on the basis of the set optimum number of teeth of each helical gear of the helical gear pair, a sound pressure level of a gear sound is compared with the sound pressure level of an audible limit with respect to a meshing frequency of the helical gear pair at a predetermined vehicle speed of an automotive vehicle in which the helical gear pair is mounted to select a frequency region in which the calculated sound pressure of the gear sound is relatively low to the sound pressure level of the audible limit, and number of teeth of each helical gear of the helical gear pair corresponding to the selected frequency region is set to an optimum number of teeth of each helical gear of the helical gear pair.

Abstract: In optimum number of teeth setting method for a helical gear pair and the helical gear pair manufactured on the basis of the set optimum number of teeth of each helical gear of the helical gear pair, a sound pressure level of a gear sound is compared with the sound pressure level of an audible limit with respect to a meshing frequency of the helical gear pair at a predetermined vehicle speed of an automotive vehicle in which the helical gear pair is mounted to select a frequency region in which the calculated sound pressure of the gear sound is relatively low to the sound pressure level of the audible limit, and number of teeth of each helical gear of the helical gear pair corresponding to the selected frequency region is set to an optimum number of teeth of each helical gear of the helical gear pair.