초록 ▼

The vibro-acoustic energy produced by an engine is reduced by shrouding the powerhead with a blanket of material that both damps vibrations and absorbs acoustic wave energy. This vibro-acoustic treatment is applied on the inner surface or surfaces of a motor housing of a propulsion system. The housi

The vibro-acoustic energy produced by an engine is reduced by shrouding the powerhead with a blanket of material that both damps vibrations and absorbs acoustic wave energy. This vibro-acoustic treatment is applied on the inner surface or surfaces of a motor housing of a propulsion system. The housing is treated by adhering a sheet of acoustic barrier material to the housing inner surface. The acoustic barrier material is designed to block transmission therethrough of a substantial portion of impinging acoustic wave energy in a range from at least 1,000 to 3,000 hertz. The layer of adhesive material has a thickness such that impinging acoustic wave energy in a range of 1,000 to 3,000 hertz is efficiently converted into heat energy. An open-cell foam core laminated to the sheet of acoustic barrier material absorbs the trapped, blocked, acoustic wave energy. The open-cell foam core has an average pore size that is optimized to absorb acoustic wave energy in a range of 1,000 to 3,000 hertz.

대표청구항 ▼

1. A propulsion system comprising:a motor; a housing encasing said motor and having an inner surface, said housing comprising an upper part and a lower part; a first vibro-acoustic treatment covering at least a portion of said inner surface of said upper part of said housing, said first vibro-acoust

1. A propulsion system comprising:a motor; a housing encasing said motor and having an inner surface, said housing comprising an upper part and a lower part; a first vibro-acoustic treatment covering at least a portion of said inner surface of said upper part of said housing, said first vibro-acoustic treatment being designed to shift acoustic energy in the frequencies between 1000 and 3000 hertz to frequencies below 1000 hertz and above 3000 hertz; and a second vibro-acoustic treatment covering at least a portion of said inner surface of said lower part of said housing, said second vibro-acoustic treatment being optimized to attenuate acoustic energy in the frequencies below 1000 hertz, wherein each of said vibro-acoustic treatments comprises a sheet of acoustic barrier material and a layer of adhesive material for adhering said sheet of acoustic barrier material to said inner surface of a respective one of said upper and lower parts of said housing.