Look around your house, car, or workplace right now and you can bet you’re not sitting too far from an electric motor of some sort or another. They’re everywhere, in toothbrushes, ovens, drills, heating systems, fans and computers, in fact you’ve probably got around fifty or so dotted around your home without you even realising.
Electric motors have been around for ages and the basic technology that makes them work hasn’t changed too much from the early 1800s, when they were first invented. Of course there’s been constant evolution and development and in 2014 we’ll see one of the most impressive results, as the entire field of Formula E cars launch from the startline in Beijing, powered by nothing other than a battery and an electric motor.
If you were paying attention in science class on the day that magnetism was explained, you’ll remember that a magnet has a ‘north’ and a ‘south’ pole. If you put two solid magnets on a table and push them together, the two opposite ends, or poles, will attract each other and the similar ends will push each other away. If you push the ‘north’ end of one magnet towards the ‘north’ end of the other, it’ll likely spin one of them round as it pulls towards the opposing ‘south’. In very basic terms, that pulling and pushing force of the magnets, where opposites attract, is at the heart of every electric motor.
Think of the pointer on a compass. If you hold another magnet up to it, it spins either towards or away from the magnet you’re holding, depending which way round it’s held.
If you were able to increase the strength of the magnets and constantly move the attraction force around the circumference of the compass dial, you’d make the pointer spin round and round as it follows it. Very simply put, that’s the way the electric motor works.
When we fix a number of these magnets around the cylindrical casing of our motor, they’re known as the stator. Place another magnet, called the rotor, onto a shaft in the centre and allow it to spin like the compass needle and the same phenomenon applies, as one side of the centre magnet is spun round as it’s attracted to its opposing pole of the fixed magnets around the casing.
However that won’t drive anything on its own, because the rotor – like the compass – will just stop as soon as it reaches the magnet it’s attracted to.
Our electric motors overcome this by making the magnets around the outside, the stator, into electromagnets. That way they can be controlled with electricity and are able to continuously swap which of their ends, or poles, are ‘north’ and which are ‘south’ at any given time.
By electronically swapping the poles of the stator around very quickly, it creates the effect of the rotor chasing the magnetic attraction round and round the inside of the motor, a bit like a dog chasing its tail in circles and hence, the motor spins.
By doing this very quickly indeed, and in a carefully controlled sequence, electric motors are able to spin very fast and produce lots of torque, or twisting force, to drive things along. In Formula E’s case a shaft attached to the spinning rotor exits the motor housing and, just like the crank shaft on a regular engine, drives the gearbox and then the wheels of the car.
With most electric cars, including the ‘hybrid’ side of Formula One, the electric motors also act as generators when the car is not under acceleration, hence the industry acronym MGU, for Motor Generator Unit.
Exactly the same technology is used, but instead of applying a current, or electricity, to the magnets turning the motor, which in turn drives the gearbox and the wheels, the rolling wheels and gearbox of the car now drive the motor and the system harvests electricity rather than using it. In motor racing circles the power regeneration process is known as ‘regen’ and just like the alternator on your road car, it generates energy to put back into the battery. So you press the accelerator and it switches on the current to the motor. The more throttle, the more current and therefore the more torque or drive produced.
Lift off the pedal as you approach a corner, the current’s switched off and the car’s now coasting, turning the motor into a generator, a bit like a dynamo on the back wheel of a pushbike powering its lights. This process begins to slow the car instantly, like an engine brake and much more aggressively than a bicycle’s dynamo, as the kinetic energy of the car’s rolling movement is turned rapidly, through resistance inside the motor, into electrical energy and fed back into the battery.
Formula E needed a fairly specific type of motor for its SRT_01E single-seater car when the idea was conceptualised. One that could deliver exciting speed and efficiency, be reliable under racing conditions and be consistent in its power delivery, as well as being small enough and light enough to fit into the tight constraints of a racing car. Like Formula E itself, it needed to be something ground-breaking and at the very leading edge of technology.
Let’s take a look at what they came up with…
The electric motor in question is an impressive piece of kit. It’s been designed and developed by a company with a formidable set of credentials in motorsport and one that I happen to know well.
I recently went back to the familiar surroundings of the McLaren Technology Centre, to talk to a man who knows more than most about this very subject.
Peter van Manen is the Vice President of McLaren Applied Technologies – the arm of the McLaren Group that takes knowledge gained through their F1 and road car programmes and uses it to pioneering effect across other businesses and industries. He’s also the man charged with overseeing the company’s significant involvement in the FIA Formula E Championship.
The electric motor, or eMotor as it’s known, along with its separate electronic control unit, are components originally created for the awe-inspiring McLaren P1 supercar. The P1 uses the eMotor as part of its hybrid system alongside a powerful internal combustion engine, but in the Spark-Renault Formula E car it’s the sole means of propulsion, meaning the demands on the unit are considerably different.
Van Manen reveals: “We started developing electric motors and controllers several years ago because we couldn’t find anything in the marketplace which was small enough and powerful enough for what we wanted to achieve in the McLaren P1.”
To put that into perspective, “you’re getting around about 5kW/kg from this motor, and that’s more than double the sorts of power densities you see in most automotive electric motors”. Hence a powerful motor with a very modest size and weight.
At about the same time as McLaren was heading towards production with their new electric motors, Formula E was being brought to life. The two got together and the beginnings of a visionary and productive relationship were formed.
It’s a relationship McLaren believes has already benefitted them greatly and will continue to do so. “We’ve already learnt a lot about electric motors with Formula E, because it’s the first time that we’ve been involved with a programme where you don’t have the luxury of an internal combustion engine to lean upon”.
Van Manen goes on to explain some of the biggest differences. He said: “An electric racing car is quite different from a hybrid because the electric motor has to do everything and it reacts instantly to driver demands. So, you have instant torque, you have instant braking. It’s quite sharp in its response so it’s quite highly strung.”
Some of the biggest challenges in the engineering of electric motors, particularly ones powerful enough to drive vehicles, come from dissipating the immense heat developed from working them hard.
The installation on the Formula E car uses a dedicated cooling system for this.
Both the eMotor and its control unit operate on high voltages and high currents and particularly in such a tightly packaged environment as a racing car, the demand for cooling is high.
Similarly to a regular single-seater racing car, radiators are mounted in the side pods, which, instead of cooling the water circulating around an engine, cool the water being pumped around the casings of the electric motor and controller unit.
Van Manen points out they are currently stretching the system’s cooling capabilities quite hard in testing at Donington Park, due to the circuit’s long straights and fast corners, which translate into long periods of full throttle and high current through the motor. “For an electric vehicle” he says, “that is the prime source of heat”.
The tracks that Formula E will actually race on once the season gets underway will be much more suited to the requirements of the fully electric race car, with shorter straights, a mixture of slow and fast corners and more of heavy braking zones for ‘regen’ and cooling opportunities. So with the units being pushed hard now, McLaren expect them to have a somewhat easier life once we start racing.
Unlike the engine in a Formula One car, there aren’t the myriad of ancillary connections, exhausts or hydraulics to worry about during installation, the eMotor’s a relatively straightforward part to bolt into the car for mechanics. It sits longitudinally in a housing, similar to a traditional clutch bell-housing, in between the battery module behind the driver and the gearbox. With just the electrical cables and two cooling pipes needed to operate it, its relative simplicity is another impressive feature.
Electric motors, together with battery technology, are two of the biggest areas that Formula E hopes to be able to develop through competition and Van Manen is keen to talk about the benefit to McLaren and the wider automotive world. ”The know-how, which is created quickly in racing, then can be read across into the automotive environment and we’re already looking at next generation road car parts ourselves, based on the knowledge we’ve gained through the P1 and Formula E, which both operate at extremes”.
He points out that the controlled environment of a race series, as opposed to the relative unknowns of McLaren’s more unpredictable, global road car customer base, do mean the technology can be pushed a little harder in Formula E.
As a result, the electric motor, nestled neatly inside the front of the gearbox casing on the SRT_01E, will launch the 20 drivers from the grid in September with staggering levels of acceleration and be part of the all-important learning and development process in Formula E’s long-term legacy.
Source: fiaformulae.com by: Marc Priestley