Noise reduction solutions for compact dishwasher

Abstract: Electrolux are currently developing a new kind of compact dishwasher, distinctly different from conventional dishwashers. A key concern that emerged through the development process was noise. The sound was characterized as loud and annoying. The goal of this thesis was to develop a mechanical design solution that would guarantee a noise level below 55 dBA. Initial tests reaffirmed the concern regarding noise. Noise was prevalent and the sound pressure level ranging from 58,8 to 59,8 was considered intolerable. Tests were performed in an acoustic lab to determine vibration source and noise factors. The pump was identified as the vibration source and the suspension was identified as the major noise factor. The rubber flange supporting the pump was fastened with screws. Loose screws failed to keep the pump in place whilst tight screws deformed the flange and pushed the pump against an adjacent plastic feature. There was a perceptible increase of 4,5 dBA when the two were in contact, and a palpable increase of 9,4 dBA when they were hitting each other. Metal spacers were the most reliable and effective solution for lowering the noise. Placed between the flange and the screws, the spacers kept the rubber flange from deforming and prevented it from hitting the adjacent feature. Metal spacers reduced the noise level from 60,6 to 51,3 dBA, a difference perceived half as loud. The efficiency of the metal washer was demonstrated in field tests, during which no complaints were made on the noise level. Pumps and dishwashers were tested in a hydraulic lab to determine operating point and best efficiency point. Pump compatibility determines performance and reliability, as poor operating conditions cause additional vibration, noise and wear. Tests concluded that the hydraulic performance and overall efficiency was poor. The operating point ranged from 4 to 8%, far below the best efficiency point of 15%. Pumps were put through a reliability test, none of which met the company requirement for longevity. Conclusions from the research were used to develop a new suspension concept. The design enabled vibrations to be absorbed and ensured infallible assembly. Rubber straps stretch between the pump and three surrounding support rods and provide supported during operation. The elastic suspension counteracts pump motion and dislocation. A prototype was manufactured to demonstrate the principle function and design.