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2. 2) M. Goto, ``Electric vehicle with the equipment emitting a warning sound,'' JP2004-322990A, 2004.11.18 (in Japanese).
3. 3) ToFiT corporation, R. Ogata, ``The equipment emitting pseudo engine sound,'' JP2011-42348A, 2011.3.3 (in Japanese).
4. 4) Japanese Automobile Standards International Centre, A Study on Approaching Warning Systems for Hybrid Vehicle in Motor Mode, Informal document No GRB-49-10 (2009).
5. 5) K. Yamauchi, ``Current trends on the audible vehicle alerting sounds for hybrid and electric vehicles,'' J. Acoust. Soc. Jpn., 68, 31-36 (2012) (in Japanese).