Dirty laundry's new spin

By: 
September 22, 1997

Every day, all year long, U.S. households wash some 77 million loads of
laundry. Almost all of these piles of dirty clothes are stuffed into top-loading
machines--washers that offer easy access and an appetite for big loads.
Unfortunately, they also demonstrate an equally big thirst, consuming 40 or more
gallons (151l) of water per single wash/rinse cycle. Added up, that's a lot of
liquid down the drain for the sake of convenience.

Maytag's high-efficiency, front-loading Neptune washer uses 40% less water and 65% less energy than conventional top-loading machines. A tilted tub and large door match top-load accessibility and ease of use.

Maytag's "dependability" engineers, working in partnership with the Electric Power Research Institute, Palo Alto, CA, have confronted this problem with the company's first-ever, front-loading washer. Built about a horizontal axis, the "Neptune" washing machine substitutes the tumbling action of a clothes dryer for the push-pull agitation of top-load machines. Tumbling clothes instead of submerging them reduces the amount of water used in the wash cycle by 12-15 gallons (45.4-56.8 l).

While environmentally-conscious consumers can rest assured the design saves considerable water, as well as the energy needed to heat that water, convenience buyers will also be pleased. Thanks to some clever engineering plus attention to ergonomics, Neptune washers offer easy access and the largest capacity of any residential washer sold today. They are also said to clean clothes better and more gently than other models on the market.

Switched reluctance motor. While high-efficiency, front-load washers are common in European households, their series-wound, universal motor with variable speed control is not readily transferable to Maytag's design requirements. One reason: Significant cost is required to upgrade a series motor to the design life requirements of the Neptune washer. Any series motor, operating at 120V in the United States, will draw twice the current required by European 240V installations.

More current means a larger commutator with bigger brushes and associated brush wear and noise--"a built-in service call," claims Maytag's Curran Cotton, VP of Research and Development, and 1996 Design News Quality Award winner (see DN 3/4/96, p. 96). Because designers wanted a maintenance-free, low-noise motor, as well as speed controllability, they turned their attention to a switched reluctance (SR) motor design.

An electronic motor controller matches the SR motor and application. Working with Emerson Electric, St. Louis, MO, Maytag engineers developed a speed/torque profile to fit the specific wash and rinse cycles demanded by Neptune. These include the high spin speeds (800 rpm Vs 600 rpm) designed to extract up to 30% more water per load, reducing the amount of water the dryer has to remove, providing further energy savings.

"We could have achieved speed controllability with a variety of technologies," Cotton points out, "but we feel the switched reluctance motor and controller from Emerson Electric is the most cost-effective and efficient method available consistent with the quality we desired."

Tuned absorber. One of the challenges in designing any washer is vibration. This is particularly true in large-capacity machines like Neptune. If unbalanced loads are not handled properly, the washing machine transmits vibrational forces directly to the floor. And if the floor resonates, so may the china closet.

Neptune, therefore, "adapts" to its structural environment. How? A simple spring-mass system, fixed inside the washer door, vibrates with the washer, but 180 degrees out-of-phase. Here's how it works:

The machine controller, which communicates with the motor controller, mounts rigidly to the cabinet. When the cabinet shakes side-to-side, so does the circuit board. An accelerometer on the board also vibrates, creating an electric signal proportional to the amplitude of vibration.

"Ideally, we want the tuned absorber's resonant frequency to be around our top spin speed of 800 rpm," Cotton explains, adding that unbalance is a product of the spin mode. As spin frequency approaches 800 rpm, the microprocessor on Neptune's machine controller monitors accelerometer output; it also monitors motor speed via tachometer feedback to the motor controller.

Once the motor has ramped to its top spin speed, the machine controller determines at which rpm accelerometer output is lowest. The motor controller then holds speed to that rpm where the tuned absorber is doing the best job at canceling machine vibrations.

Conservation and convenience. Two other features differentiate the Neptune washer from European front-load designs: 1) a 15-degree tilt to the wash basket, and 2) a 15-inch diameter tub opening.

Maytag's marketing people evaluated competitive front-load washers and found them hard to load. Consumer studies agreed--the public felt they had to bend and stoop too much, and were not happy with the smaller European-like door openings. Maytag engineers solved the problem by tilting the stainless steel tub to improve visibility and reach; by designing the cabinet, top cover, and door to interface with the tilted tub; and by expanding tub opening diameter. The latter required working with Medibeg of Belgium to manufacture the industry's largest rubber door boot.

"We've known for a long time that European high-efficiency washer technology has held promise with its cleaning ability as well as energy and water savings," concludes Cotton. "But we also knew there were certain features, such as capacity and accessibility, that North American consumers weren't willing to sacrifice. With a significant investment in tooling and targeted consumer research, we are debuting the best of both worlds in the Maytag Neptune washer."


Maytag's motor of choice

Switched reluctance motors feature rugged construction, few parts. Operating principle is equally simple: Applying current to opposing stator windings creates a flux that attracts opposite rotor poles, producing torque.

Not only do SR motors eliminate the wear and electrical interference problems normally associated with brushes, they are physically smaller than comparable ac motors, reverse without relays, and operate over a wider speed range.


Clean but green!

by Roy O'Connor, European Bureau Chief

German cleanliness is legendary, but in recent years environmental aspects have also loomed large on the horizon, affecting both domestic and industrial issues. How does one get clothes clean with the minimum environmental impact? AEG Domestic Appliances point to their Oeko Lavamat front-loading washer.

In this washer a smart, micro-computer controlled DC motor drive and neuro-fuzzy logic provide the intelligence and expertise needed for single-knob operation. The development objective was to obtain a washer efficient in terms of energy, washing agents, and water--not just at the nominal mixed-wash load of 5 kg, but also with loads down to 1 kg.

Because it is smart enough to decide how many rinses and how much water it needs for different loads, the washer only needs 48 l and 0.94 kWh of electrical energy for a standard 5 kg load. For a 1 kg load the washer gets by with just 20 l of water.

Once the program has been selected, fuzzy logic determines how much laundry has been loaded. This is done by soaking the clothes with a small amount of water which is then spun out again. Level measurement, comparing the volume of water extracted to that originally added, gives a measure of the weight of clothes loaded. This figure determines the number of rinses and the amount of water needed.

For the washing cycle itself, a four-jet spray system in the drum ensures that clothes are soaked right through to the center of the bundle. After about ten minutes, once the washing enzymes have done their job, a stain removal agent is added. This process allows the washer to use a lower temperature of 40 C compared to the standard 60 C for a mixed wash, giving corresponding savings in energy.

AEG employs their Advanced Rinsing Technology (ART) to the rinsing cycle. Once rinsing has lowered the suds concentration to a level where foaming is reduced, ART's intensive spinning helps reduce the amount of water needed to 10-12 liters for a 5 kg load.

Apart from optimizing the washing cycle, on-board fuzzy logic also helps reduce vibration by detecting down to 600 grams of unbalance during the spin cycle. This also helps save energy, because the washer can then spin at the relatively high speed of 1600 rpm, reducing drying time.

Comments (0)

Please log in or to post comments.
  • Oldest First
  • Newest First
Loading Comments...