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2017-09-22

As electric motors improve, more things are being electrified




HENRY FORD may have brought motoring to the masses in 1908 with the Model T, but his wife, Clara, preferred to drive an electric car. Combustion engines were noisy, dirty and in their early years required hand-cranking to start. Mrs Fordís 1914 Detroit Electric, however, moved away instantly, was nearly silent and its speed was easy to control by pushing or pulling on a wooden rod that selected the required amount of power from a bank of nickel-iron batteries. Her car could travel for about 80 miles on a single charge and exceed speeds of 20mph.
Mr Fordís mass-production techniques soon cut a Model Tís price to $500óone seventh that of Mrs Fordís car. As refuelling stations spread, the internal-combustion engine went on to conquer all. Now electric cars are cruising back, as performance improves and costs fall. Teslaís new Model 3, for instance, reaches 140mph and its lightweight lithium-ion battery has enough juice for 300 miles. But it is not just better and cheaper batteries that are changing the economics of electrification. Electric motors are getting better, too.
This matters because electric motors are everywhere. The International Energy Agency reckons they consume more than 40% of global electricity production, twice as much as lighting, the next largest user. Electric motors power running machines in gyms and baggage-handling systems in airports; they run air-conditioning in homes, lifts in offices and robots in factories. In the future, besides electric cars, they will increasingly take to the sea in ships and start propelling aircraft.

Enter the black box

At the moment, many electric motors are still run at a constant pace, relying on mechanical systems such as gears to step that up or down to provide whatever speed is wanted by the widget to which they are attached. That is wasteful, and engineers are working to improve things. In electric cars, for instance, the job done by gears (or the wooden stick in Mrs Fordís ride) is already performed by a box of electronics. This is increasingly true of non-car motors, too.
A modern electric motor and its associated drive system can produce the same amount of power as one from 1910, but in a package that is a fifth the size, says Andrew Peters, who runs Siemensís drive factory in Congleton, in the north-west of England. The latest designs are extremely efficient: some big electric motors can now turn 97-98% of the electricity put into them into mechanical energy. Even the best internal-combustion engines can manage only about 45%. Small gains in efficiency mean big savings in cost, says Mr Peters. The cost of an electric motor and its drive represents just 1-1.5% of the cost of the electricity it will consume over a 20-to-25-year operating lifetime.
Much of the efficiency boost comes from highly precise modern manufacturing techniques, as well as advances in materials science. Electric motors waste energy mostly in the form of heat generated in their windings, which are coils of copper wire wrapped around a metal core. Several such coils form the rotor, which is the part of the motor that turns, and which sits inside the stator, which does not.
Electric motors work by sending electricity through the windings. That turns them into an electromagnet, generating a magnetic field which pushes against an existing field generated by a second set of permanent magnets inside the stator. That causes the rotor to turn until it has aligned itself with the magnetic fields. To keep it turning, and make a useful motor, those magnetic fields must be constantly changed. That is done by switching the direction of the current in the windings.
In a motor using direct current, which comes from a battery, the switching is done with a commutator, a type of mechanical switch. The commutator is attached to one end of the rotor, and picks up power from stationary ďbrushesĒ as it turns. These brushes, usually made from soft carbon, are infamous for burning out in electrical appliances.
These days, though, brushes are not necessary. In newer motors the usual order of things is reversed, with the windings held in the stator and the rotor sporting permanent magnets. The current in those windings can then be switched electronically. Eliminating the brushes improves reliability, and electronic switching offers much finer control than the old mechanical system. The permanent magnets can be improved, too, by making them from strongly magnetic rare-earth materials such as dysprosium and neodymium.
Other designs are also being used. One is the switched reluctance motor, a nearly 180-year-old idea given a new lease of life by drive technology. A reluctance motor eliminates the permanent magnets as well as the brushes. Instead of relying on opposing magnetic forces to generate torque, it uses another property of magnetism, called reluctance, which is analogous to resistance in an electrical circuit.
In such a motor, the magnetic field produced by the energised windings follows a path of least reluctance through a rotor made of iron. The rotor turns to align itself with the field in an attempt to reduce reluctance to the minimum. Constantly switching the current forces the rotor to turn repeatedly. Since they sport few parts and use base materials, reluctance motors are cheap; they deliver high levels of torque.
Visedo, a Finnish company, has taken the idea even further with a synchronous reluctance-assisted permanent magnet (SRPM) motor. One of the downsides of a reluctance motor is that to deliver a given amount of torque it needs to be larger than an equivalent permanent-magnet motor. By reintroducing magnets Visedo gives the reluctance motor extra oomph, which means it can be made smaller but still able do the same amount of work. The SRPMs are liquid-cooled to make them more efficient and, says Kimmo Rauma, Visedoís boss, are particularly suitable for heavy-duty operations.
The company has put its SRPMs in a fleet of electric buses in Helsinki, in industrial equipment such as excavators, and in agricultural machines and ferries. Some machines are hybrids, with the electric motors used alongside internal-combustion engines. That still produces large fuel savings and reductions in emissions. Earlier this year a Visedo system was installed in a 100-tonne hybrid ferry in Kaohsiung, Taiwan. The vessel, which carries passengers to and from an island popular with tourists, uses a diesel engine for only part of the time. The ferry connects to a fast charger to top up its batteries when loading and unloading.
Electric motors are also taking to the sky. Most drones are powered by brushless motors; similar kit has also found its way into microlights and, more recently, light aircraft. Their high torque is ideal for turning propellers or ducted fans (a circular set of blades contained within a shroud). Though batteries add weight, some of this is compensated for by the simplicity (and therefore lightness) of electric motors and by the removal of unnecessary parts such as gearboxes.
Lighter electric motors are now being developed specifically for aviation. Siemens, for one, has put an electric motor into a stunt plane made by Extra, a German firm. The plane has set a number of records, including being the first to tow a glider aloft. Boeing, Airbus, Rolls-Royce and General Electric have various electric-propulsion systems under study. One idea is for hybrid planes seating about 100 passengers that would take off and land using jet engines, when most power is required. During the cruise jet engines are throttled back, so for that stage of the flight the plane would use electrically powered ducted fans instead.
As for Mrs Fordís Detroit Electric, the Anderson Electric Car Company, which owned the brand, stopped selling cars in 1939. But the Detroit Electric name has been revived by Albert Lam, a former boss of Lotus, a British sports-car firm. Having established bases in Britain and China he plans to bring a number of electric vehicles to market over the next three years. Clara would have been delighted; Henry perhaps less so.