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issue: October 2008 APPLIANCE Magazine

Dishwashers
Sound Dishwasher Design


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by Lisa Bonnema, senior editor

Dishwasher engineers are falling back on their mechanical expertise to fine-tune today’s high-tech designs.

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Vestel White Appliances has designed a patented device for adjusting the height of the upper basket in dishwashers. The mechanism, available on models sold across Europe, is molded using high-performance polymers from DuPont Engineering Polymers.

There’s no question that advancements in electronic motor and sensor technologies have brought appliance design to new levels of innovation. Cost savings, convenience features, and energy efficiency can all be attributed to these two critical component technologies. But that’s only part of the design story.

At the engineering table, all aspects of design need to be investigated to develop a product that performs to consumer expectations. While many appliance companies have heavily invested in electronics R&D, engineers are finding that there is still a lot to be said for tweaking mechanical designs. Using a variety of in-house techniques, dishwasher engineers are addressing core design issues like noise, cleaning performance, and ergonomics to build quality machines from the ground up.

Keeping It Quiet

One design aspect that continues to be a focus for dishwasher engineers is noise. According to John Dries, president of Dries Engineering (Louisville, KY, U.S.; www.driesengineering.com), this takes a considerable amount of design work. “The days of just throwing an itchy fiberglass blanket on a plastic tub and declaring it good enough are over,” he says. “We are now at a point in dishwasher evolution where the best dishwashers simply cannot be heard in a normal kitchen with normal background noise.”

Dries says that in order to successfully manipulate sound levels, today’s development engineers need to become experts in noise control. “That means understanding how the noise level is measured and computed, and becoming an expert in structural dynamics and other noise control strategies,” he says.

Richard Allen, product manager for Asko Appliances (Richardson, TX, U.S.; www.askousa.com) believes that the key to quiet design is building dishwashers on a solid foundation that minimizes vibration. “Asko dishwashers all begin with a solid one-piece galvanized-steel base pan,” he tells APPLIANCE. “The circulation pump is the only component that makes contact with the base pan, through a single rubber post. On top of that solid base pan rests a ribbed stainless-steel tub. All of our dishwasher tanks come wrapped with bitumen. Step-up models also feature a woven felt insulation on top of the bitumen for further noise reduction.”

AB Electrolux addresses vibration by using independently isolated components in its dishwashers. “We found this to be the most effective manner to isolate vibration and still allow for ease of service if required,” says Troy Dalsing, advanced R&D manager for Electrolux Major Appliances Dishwasher Division (Stockholm, Sweden; www.electrolux.com).



Many dishwasher engineers are choosing stainless steel for filter media, as shown in this Bosch main filter. “Tooling for plastic filters is too costly to maintain and often provides inconsistent part quality,” says Mike Edwards, senior design engineer, BSH Dishwasher Division.

Martin Kornberger, head of R&D Dishwasher Domestic, Miele & Cie KG (Gütersloh, Germany; www.miele.de), says that the first design priority should be optimizing the vibration source itself, namely the driving unit of any pump. “Intelligent motor designs which offer silent operation are nowadays possible,” he says. “But secondary measures like a suspension system with adapted vibration-transfer characteristics, as well as classical damping materials, are still essential and effective.”

BSH Home Appliances (Huntington Beach, CA, U.S.; www.bsh-group.us) minimizes vibration by using rubber straps to suspend motors and pumps. Mike Edwards, senior design engineer for BSH’s Dishwasher Division, says the company also uses specially designed seals at the connection of the pump/motor to the sump. “The goal is to isolate the pump/motor systems as much as possible, so that vibrations cannot be transferred to other components,” he explains. “Reduction of motor noise is necessary to produce low-noise dishwashers.”

Drain noise associated with the drain pump is also a concern. However, Allen of Asko believes that most of the drain noise consumers are hearing is from the sound of water entering the home plumbing. “Most dishwasher manufacturers have reduced drain noise through insulation and vibration dampening,” he says. “In many cases, the only way to reduce the sound of water flowing through the home plumbing would be to reduce the rate of flow. Drain systems have to be designed to handle all of the challenges that restrictive home plumbing presents. Reducing drain flow at the cost of drain performance isn’t a viable option.”

Kornberger of Miele says the most important issue is proper installation at the sink. “Often, the drain hose of the dishwasher is connected above the odor-sealing bend, directly beneath the sink,” he tells APPLIANCE. “Beside detergent odors, gargling noise is the consequence, directly transferred into the kitchen. On the machine side, new techniques are available to ensure that the drain pump immediately stops if the water is drained to avoid unstable pump conditions.”

Edwards of BSH agrees that most of the draining noise escapes from the sink. “Considerable improvement can be achieved by having the household plumbing provide a special drain connection for the dishwasher with the required plumbing vent routed to the outside,” he says.

Airborne noise coming from the spray of the wash system is another area that engineers are addressing. One strategy is to make sure dishwashers are airtight. “Any opening on the front of the dishwasher must be closed to reduce the noise transmitted into the room,” Edwards says. “Good sound-absorbing insulation must be used in the dishwasher construction. The use of elastomer seals to close gaps at problematic openings on the dishwasher must be employed. The same sealing philosophy is used to close any openings between the dishwasher itself and the cabinet or floor.”

Chris Roberts, senior systems engineer at GE Consumer &
Industrial (Louisville, KY, U.S.; www.ge.com), says that another tactic is to use a damper in the vent that closes during the wash and rinse portions of the cycle. “This allows for noise reduction while the water is circulating and adequate venting during the drying phase,” he says.

While quiet operation is an important feature for any kitchen appliance, Kornberger of Miele adds that engineers need to remember that consumers actually expect some level of noise. “Today, our dishwashers are so silent that you can barely perceive them in a normal household environment. People may even find this irritating—thinking the machine is defective or inefficient,” he says. “The question for sound designers must be whether it makes sense to hear the dishwasher, but with a smooth, positive sound instead of [an] annoying [sound].”

Keeping It Clean

A new tall-tub dishwasher from Fagor America is designed to be exceptionally quiet at 45 dBa. This is enabled by an alternating wash function, with alternately operating sprinklers that also make the dishwasher more efficient. Noise is also reduced by the insulated interior and by a solid inner tub designed to have no seams.

When addressing cleaning performance, the design of the dishwasher filtration system is critical. Should the system be submerged during the wash? Should it be exposed? Or should it be even with the operating water level?

Edwards says that in BSH dishwashers, the operating water level is just below the filter. “A balance must be achieved between reducing the amount of nonproductive water (dead water) and providing enough water to maintain constant flow to the pump,” he explains.

Kornberger agrees, but adds that it might be useful to alter the water level during the washing process. “Here, each manufacturer has their own know-how and strategies,” he notes.

Allen believes that the filtration system should be multilevel to trap different types of debris. “At minimum, one level to strain the surface of the water as well as one lower level to trap the larger items that find their way into the sump,” he explains.

Electrolux uses a similar approach with its three-level filtration system. “The coarse filter and trap in the new Electrolux dishwashers are positioned at water level or slightly below, and the pressurized fine filter is positioned above the water line,” he tells APPLIANCE. “Having the coarse filter and trap at water level or slightly below facilitates movement of large particles toward the drain. Having a pressurized fine filter above the water line promotes efficient self-cleaning.”

Keeping the filter clean during the wash is another challenge. Edwards says the key is proper selection of filtration material and the addition of “clean-off” nozzles to the spray arm. “Improperly designed holes in the filter can trap food soil,” he explains. “‘Clean-off’ nozzles attached to the spray arm provide 360-degree coverage.”

Dries agrees that filter material is critical and that rough edges and funnel-shaped holes greatly increase the tendency for food to get stuck on the filter. “A common quality mistake in the manufacturing of stainless [steel] filters is to load the pre-punched or etched metal in the forming die upside down,” he says. “It looks fine, but it can cause the dishwasher to completely clog when it is run with a large dish load.”

KitchenAid achieved its quietest dishwasher design ever with the EQ Wash System and Whisper Quiet Ultima Sound Insulation System. The result is a sound rating of only 48 dBA, per IEC standards and operating in the normal cycle. This is a level close to that of a quiet room (about 40 decibels). A variable-speed motor helps minimize operating noises by starting slowly and adjusting its operating capacity to deliver the power needed based on the wash cycle. Alternating wash zones focus washing action while using less water and energy. Debbie O’Connor, senior manager of brand experience for KitchenAid, says the dishwasher is 58% more efficient than Energy Star. “It also has an efficiency designation from the Consortium for Energy Efficiency (CEE), making it eligible for energy rebates in select states,” she says.

To keep food from flowing back into the filter media, Edwards of BSH says the drain pump should be started before the circulation pump is stopped so the majority of the food soil is drained while reducing the amount of water in the sump.

Asko uses separate circulation and drain pumps as well as multistage filters. “The Asko two-pump setup means the drain pump draws from inside of the filter,” Allen tells APPLIANCE. “Our self-cleaning system cleans the filter assembly and regenerates the wash water during the prewash cycle.”

In its latest dishwasher models, Electrolux focused on tweaking the design of the holding chamber for food soils. “We developed a specialized drain feature incorporated into the holding chamber that bleeds and filters the water off the top of the holding chamber, creating a flow to retain the soils,” Dalsing says.

Keeping It Convenient

Mechanical design is also being used to add convenience to dishwasher designs. Turkish appliance maker Vestel A.S. (Manisa, Turkey; www.vestel.com.tr) has designed a patented mechanism that allows customers to adjust the height of the upper dishwasher baskets.

The mechanism is based on four principal parts—a base plate, rail plate, fixing plate, and cog. The base plate, which is securely attached to the dishwasher’s upper basket using snap-fits, interlocks with the rail plate. The rail plate has integral wheels that fit within the dishwasher rails and enable the basket to glide in and out for easy loading. Between the two plates, which slide above each other in a vertical motion, is a fixing plate. It contains a star-shaped, rotating cog that locks the basket in place at the desired height.

“The principal function of the adjustment mechanism is based on mechanical motion,” explains Orhan Hülagü, research and development engineer at Vestel’s dishwasher factory. In the basket’s lowered position, the cog rests against a long, thin raised section on the base plate. When the basket is pulled upward, the cog is rotated by interaction with a second, rounded, raised section at the bottom of the plate, which also limits its upward movement. As the basket is released, the cog catches on the bottom of the thin section, and the basket is locked in place by its own weight. When required, the basket is lowered by releasing the cog through an upward movement, which allows the basket to drop to its resting position.

Hülagü says that unlike competitive height-adjustment mechanisms, Vestel’s device doesn’t require extra handles on the sides of the basket. “Our patented mechanism allows users to smoothly adjust the height of the upper basket of [our] dishwashers, regardless of where they hold it,” he tells APPLIANCE. “There is no need to push or pull any handle.” The mechanism can also be adjusted even when the upper basket is full.

During the design phase, Hülagü says Vestel engineers focused on addressing the stiffness of the mechanism under heavy loads. Durability was also important since the device would obviously be exposed to high temperatures, humidity, and detergent. “Therefore, the choice of materials for this mechanism was important,” Hülagü says.

The appliance maker trialed several polymers, most of which had problems with warping and hindered the mechanism’s operation. Materials from DuPont Engineering Polymers, however, provided both the strength and dimensional stability the company needed. Specifically, Vestel used two engineering polymers from DuPont. The base plate, rail plate wheels, fixing plate, and cog are all molded in a low-wear, low-friction grade of Derlin acetal resin, while the rail plate is molded in a stiff grade of Minlon mineral-reinforced nylon. “With a large degree of interaction between the two materials, their low noise and low friction performance when in contact with each other add to the overall convenience of the system,” Hülagü says.

A Solid Foundation

There’s no question that over the last few years, most of the buzz surrounding appliance design has been on technological advancements. But the fact remains: Good design is based on good design. An efficient motor doesn’t compensate for dirty dishes, and sensors don’t muffle a noisy drain pump. Today’s dishwasher engineers need to be careful to focus on building a solid foundation before adding all the bells and whistles. Doing so can mean the difference between a machine that sells, and a machine that ends up back on the drawing table.

 

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