23 April 2012
All electric racing car utilises breakthrough technology
The sheer amount of technology transferred from the motorsport sector is hard to beat. From advanced materials to sensor technology, innovations developed for the track often end up in everyday road cars, as well as in applications radically different than intended. Indeed, only the aerospace and defence industries can compete in terms of technology transfer.
It is therefore exciting when a premier UK motorsport manufacturer teams up with the former Minister of State for Science and Innovation to develop and race the LMP1; an all electric Le Mans Prototype car.
"We see a tremendous business proposition and opportunity," says Lord Drayson, managing partner at Drayson Racing Technologies and current president of the Motorsport Industry Association. "I am certainly not doing this as an enthusiast."
Lord Drayson has long been an advocate of introducing cleaner technologies to motorsport, beginning with a bioethanol powered Aston Martin DBRS9 car in the 2009 British GT Championship, followed by a 'flex fuel' LMP1 car in 2010, developed in association with Lola and powered by a Judd V10 engine.
"We raced that very successfully and came third in the Intercontinental Le Mans Cup behind Peugeot and Audi," says Lord Drayson. "And we got the first ever win for a biofuelled car. Coming at it from a transferability and proprietary technology point of view, we are working with Aston University on some interesting technology around pumps for biofuels. We think this is going to be a very interesting new product and has come directly out of racing experience."
The next stage for Lord Drayson on his quest for cleaner motorsport is the development of the Lola-Drayson B12/69EV, an all electric LMP1 racing car. While the chassis is that of the 2010 Lola LMP1 series car, everything underneath the bodywork is new.
Angus Lyon, chief engineer for the electric drive train, says the car has been designed from first principles. "The first thing was to make sure the car was designed properly and not lashed together. We started at the architectural level from the electronics and software points of view, optimising for simplicity. But we also needed the correct balance between active systems and passive systems that work independently of sensors and similar components. A lot of time was spent on lap time simulation to work out the base specification; the motors, batteries and aerodynamics."
One of the major areas of interest was the communications design. Lyon notes that a lot of time was spent optimising the various communications systems, such as the CAN hardware. "We've looked at this from an interface perspective and how to manage it. Even CAN bus termination can't be ignored," he says. "It must fall within acceptable limits."
The integration phase followed; pulling together the motors, the batteries and the charging system. Control units have been supplied by Cosworth, but the software has been written by Drayson to a detailed Tier 1 control specification. "That defined everything, including the algorithms which control the car," Lyon adds.
The design has been through a number of optimisation processes and this has turned up a few surprises. "Typically, the high voltage components used in electric vehicles tend to be overdesigned," Lyon claims. "When we started to do thermal simulations, we found we could 'wind down' the wire gauge quite a lot; to the point where we saved 20kg from the high voltage cabling." But that effort also highlighted the inter relationships. "When you do this," Lyon admitted, "you see how each component works with the others; for example, the bus bars can help with cooling fuses."
Being used for the first time on the car are lithium iron phosphate batteries developed by A123 Batteries. These are said to give the necessary power and energy density – equivalent to an 850hp engine – required for racing at speeds up to 200mph.
The 30kWhr battery pack supplies power at 700V, providing the equivalent of 850hp for five minutes. "Less if there isn't cooling off time," Lyon pointed out. Peak currents in the car can reach 1400A dc, with ac currents reaching 350A.
To facilitate quick battery charging, Drayson is working with HaloIPT, recently acquired by Qualcomm. HaloIPT is developing inductive power transfer (IPT) systems for charging electric vehicles wirelessly, but is also working on powering cars as they race around the track.
The partnership aims to pioneer the deployment of dynamic (in motion) charging of zero emission electric vehicles. Racing cars fitted with HaloIPT's technology will pick up power wirelessly from transmitters buried under the road or race track surface, ensuring the vehicle receives power on the move.
Dr Anthony Thomson, HaloIPT's chief executive, says: "We are excited to be transferring this expertise to the electric vehicle market. The deal with Drayson Racing demonstrates the appetite for technology that makes driving an electric car more convenient and this is certainly the case in the motorsport sector – nothing could be more convenient than a race car that refuels itself on the track."
Lyon says that, while inductive charging technology had been around 'for years', HaloIPT had taken it to a new level. "The system started out delivering up to 7kW at 80% efficiency; now, it delivers 20kW at 92% efficiency."
The yokeless and segmented armature motors have been developed specifically for this application by YASA Motors, a spin out from Oxford University. Four YASA-750 axial flux motors will propel the car. The step change in the specific torque of the motor is 30 to 40Nm/kg – at least twice as good as the best alternatives – and comes from the combination of patented improvements in magnetics, cooling and packaging.
The direct drive motor, which measures 350mm in diameter and 70mm wide, fits within the space typically occupied by the front or rear differential of a regular vehicle. The 25kg motors give a peak torque of 750Nm and a continuous torque of 400Nm.
"We have four of those motors: two on each wheel, so there is plenty of torque," says Lord Drayson. "There is no differential; it uses a single reduction gear to match the speed of the motors to the wheels. We then had to look at other systems on the car, such as regenerative dampers; another key factor for this type of race car. That is another area where the technology specific to our needs didn't exist, so we spent some money on R&D and turned it into a product ourselves."
In fact, the drivetrain at the rear of the car can be considered as two halves. Because both sides are independent, the team can apply torque vectoring techniques. "While a mechanical differential distributes torque equally, we go beyond this and drive the wheels actively. This allows us to effectively steer the car; during acceleration, for example," Lyon says. "We can get the handling balance how we want it." The system also helps with optimising regeneration.
Field oriented techniques are used to control the motors. "This is very robust to the high emc fields generated in electric vehicles," Lyon notes. Contactless eddy current sensors are also used on the motors and are complemented by a range of more conventional Hall Effect type sensors, as well as voltage and temperature monitors. "EMC has been one of the big problems with electronic systems in Formula 1," said Lyon, who developed electronic control systems during his time with the Brawn and Renault F1 teams.
Overall, the project relies upon optimisation. "We're pushing things to the limit," said Lyon, "everything from aerodynamics to cabling. We have to work out what are the best combinations. For example, we might lose 5kg from the cabling, but dissipate more energy. That would mean less power gets to the wheels. We have had to develop techniques that helped us to understand the best compromises."
The development of the car coincides with an announcement last year by the FIA of a new World Championship exclusively for electric cars; the FIA Formula E Championship. From 2013, all electric machines will race around city centres on street tracks.
The series will be made up of short races, partly because of the technology's limitations, but also because it is believed the format will appeal to a new generation of fans. These short races will have a number of heats – at the moment planned to be 15 minutes long, with a 30 minute charge time in between. Although this sounds relatively short, the power required to race at speeds of up to 200mph for 15 minutes at a time is really pushing the boundaries.
Part of the idea behind the proposed Formula E series for electric vehicles is they will recharge between races while in the pits. For optimal charging, the car must align precisely over contact pads, but Lyon says HaloIPT's technology is more tolerant to misalignment. "It makes it easier to park the car and makes the technology more suitable for dynamic use."
When it comes to powering vehicles on the move, HaloIPT's technology can adjust automatically for the changing vertical gap between car and track. The system can distribute power intelligently, ensuring consistent delivery of power at high speed.
Lord Drayson says: "Dynamic wireless charging will be a game changer, enabling zero emission electric vehicles to race over long periods without the need for heavy batteries. Motor racing is the ideal environment to fast track the development of this promising technology and to prove its effectiveness. This milestone innovation will have a dramatic effect, not just on racing, but also on the mainstream auto industry. We're looking forward to putting this technology through its paces."
Like other series of motor racing, particularly F1, the UK has an opportunity to be a leader in developing the technology and innovations which in turn should filter down in to the more mainstream engineering world.
"It is important that Britain invests in these future technologies and manufacturing capacity which is a really good strong growth area," says Lord Drayson. "The technologies that we are innovating here from racing activities are applicable to many other sectors; aerospace, clean energy, marine all need technologies that are, for example, lightweight, use new materials or have embedded sensors."
While motorsport will keep a very close eye on these developments, so too should UK engineering; seizing the opportunities offered by the technology and taking inspiration from its success.
For the moment, development of the electric LMP1 remains predominantly an on screen activity, although the various components continue to be tested. "We're still going through the validation process," Lyon concludes. "The first test of the complete car will take place behind closed doors, but I think we should be able to demonstrate it on track in July."
Justin Cunningham and Graham Pitcher