brush motors
Motor technology of the 1970s - induction motor or universal (brush type) motor. Induction motor, as used in USA top loaders, operates at a fixed speed (or possibly two fixed speeds if it has two windings inside).
The USA style two speed motor has two speeds that aren't hugely different - usually something like 3200 rpm and 1600 rpm. (Sorry if these numbers are a bit out - I'm Australian so more familiar with 50HZ supply, so our equivalent motors are 1440 rpm / 2880 rpm.) So a ratio of 2:1 between motor speeds. This is easy to achieve but useless in front loaders, where you require around 10:1 ratio between slow and fast motor speed - for wash speed the drum tumbles around 50 rpm, spin speed should be at least 500rpm at the drum. So many early front loaders had a mechanical transmission to give the two different drum speeds, but this adds weight, cost and complication.
A few lower priced European front load machines also used two speed induction motors, but a limitation of the technology means these machines had a miserably low spin speed, usually about 400 rpm. The two speed motors for Euro front loaders were huge and heavy, which took up space inside the cabinet. In their favour, they were simple and reliable. The two speeds (at the motor, not the drum) were 2880 fast speed (for spin) and about 360 rpm for Wash. this is a ratio of 8:1 so when the pulley sizes are engineered to give a wash tumble speed of 50 rpm, the spin will be 400 rpm. If you alter the gearing for a faster spin, the wash tumble will be too fast and the wash performance will be poor - the clothes will go round and round but never flop down in the tumble.
In the early 1980s some European machines had a variable diameter pulley on the motor, so when the motor stepped up to spin speed, the pulley diameter increased which got the spin up to a dazzling 800 rpm. These motors were huge, heavy and the variable diameter pulleys proved to be not very reliable.
The better performing alternative was to use a universal motor, which uses brushes. Like the motor in an electric drill. These are more compact, more efficient, and have infinitely variable speed with electronic control. So suddenly it became easy to design a washing machine that washes at 50rpm and spins at 1000 rpm or even more. This adds a cost in that you now need an electronic control module, and brushes wear down so you need brush replacements over time. In 1970s technology these are more noisy, too. (This improved over the years.) But the increase in performance is fantastic, and you can have improvements like the option of several spin speeds, and a special speed to balance the load before spinning, called Distribute. You can gradually ramp up the speed instead of jumping from wash to spin, so load balancing is easier and more effective. The motors can be much smaller, saving space (thus allowing a bigger drum) and weight.
Philips developed a similar technology using a permanent magnet motor, this still uses brushes but is even smaller and lighter, and can be more efficient, though Philips' early control circuitry was terribly inefficient, being designed more to reduce cost than save energy. they were very reliable, too. the Philips machines had infinitely variable spin speed, set by a simple dial, up to the max of about 1000 rpm.
Plenty of current front loaders use similar motors to these 1970s brush motors, though the electronics driving them is way more efficient now. I have recently acquired a Miele from about 2010 that still uses a brush motor, though it is very quiet, efficient and has varying speed wash tumble and very fast spin speeds. (1400 rpm drum speed on spin.)
the new technology these days is electronically controlled 3 phase motors (driving a 3 phase motor off a single phase supply using clever electronics) and brushless direct drive like F&P Smart Drive (which I think are also a different form of 3 phase, or perhaps brushless DC?) These are even more efficient, have an even greater range of speeds, don't have brushes to wear out, arc, get dusty and so on.
So that's why brushes.....
Chris.
lD
