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Less is more: Formula One engines are shrinking, with greater emphasis on energy conservation and battery technology transfer. John Mortimer reports on developments under way at Mercedes.

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Arrogant, outrageous, self-centred, wasteful and extravagant. Just a few of the words that some might use to describe Formula One racing. But the seeds of change have been laid under new rules from the sport's governing body the FIA. From 2014 onwards these should contain some of the excesses of cost and energy consumption as well as transferring more technology to road-going vehicles.

Tucked away in rural Northamptonshire, engineers at Mercedes AMG High Performance Powertrains are meticulously planning for this new future, having finished 2011 as the top-scoring engine maker with 100 podiums.

So the Mercedes engineers are working on their new F1 engine. But they are conscious that fewer engines will be required in the future as the number allowed per driver each season could be halved by 2015.

Halving the output of engines made would have profound knock-on effects for the facility at Brixworth and its 450 top-flight engineers. The solution, ironically, has emerged from the kinetic energy recovery system (KERS) used in 2011.

Mercedes' F1 KERS, weighing 24kg, uses high energy density lithium-ion batteries. Brixworth is now the nerve centre for developing bespoke battery systems for the SLS AMG E-Cell high-voltage gullwing electric car based on this race technology.

Design and development work on the batteries began at Brixworth 18 months ago and production will start in early 2013. This is just one dramatic technology transfer from F1 's 2011 season. Others will emerge from the 2014 race engine, according to engineering director Andy Cowell.

Cowell carefully skirts around technical details, wary that any unguarded comment could alert competitors. He has no wish to compromise himself.

"The main challenges are internal combustion energy efficiency and energy transfer," he says. "In effect, KERS will become ERS."

In last season's KERS the motor generator unit (MGU) is gear-driven from the crankshaft. On braking, power electronics convert AC from the MGU into DC to feed into the battery. For acceleration the process is reversed. The system has 80% efficiency, so, of the 500kJ captured, 400kJ is released, giving a 6.75s boost at 60kW.

Under the 2014 rules, the engine will be a turbocharged 1.6-litre V6, compared with the present 2.4-litre naturally aspirated V8. According to the new FIA rules the turbocharger shaft must be parallel to the crankshaft and no more than 25mm from the crankshaft centreline, which itself is on the centreline of the car.

"If we had complete freedom, we would have two turbochargers--one for each bank. But that would double the cost," says Cowell. "In terms of cost and technology constraints, all the teams will be in the same boat.

"However, we have agreed the freedom to develop our own aerodynamic surfaces within the compressor and turbine.

"And to harvest energy from the engine we are permitted an electric machine coupled to the turbocharger shaft. In that way we can compound energy from the turbine, not mechanically but electrically back into the system. So, KERS becomes ERS.

"In 2011 we recovered energy kinetically under braking," explains Cowell. "In the future we can recover energy under braking also but with a 120kW electrical machine, rather than today's 60kW machine. And we can recover energy waste heat from the exhaust system through the turbine. The value is free."

This raises the prospect that both wastegates and intercoolers could be used. Cowell says nothing. But he notes that it is up to engine makers to decide the power level recovered from the turbine.

"There is a balance to be struck," he declares. "If you recover energy at a high rate, i.e. at a high power level, the back pressure on the exhaust system will be high; the turbine will be more of a restriction and the internal combustion engine efficiency will be affected. So we have got that balance to work out ourselves."

According to Cowell, the turbine will recover energy using the aerodynamics of the volute and the design of the turbine wheel. "So, instead of just driving the compressor, the turbine can also drive an electrical machine," he says. "There is one turbine and one compressor. It is a fixed geometry design without any of the variable features developed for a road car."

Besides recovering up to 120kW, the system can transfer 2MJ and put it into battery storage using the kinetic system. The battery pack will weigh 20-25kg. Fuel will be limited to 100kg.

"We can recover as much energy as we like from the electrical machine on the turbine but we can only propel the vehicle using the 120kW electric machine (wherever you want to put it) and with energy per lap of 4MJ. That is 10 times the energy used to propel cars today, but through a machine that is double the power and five times the duration."

Cowell adds that 30s or so duration at 120kW, if the system operates at that level, brings it to the point where electrical propulsion is used for nearly the same period as the internal combustion engine. This could lead to spin-off for production cars.

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Other aspects of the work at Brixworth that could lead to spin-offs include the use of materials, downsizing, downspeeding and gasoline direct injection.

The battery pack has maximum and minimum values for storage. This is to prevent development of costly and very high energy density systems.

There are also minimums and maximums for the entire power unit, a minimum centre of gravity position, fixed engine mounting positions, and the engine crankshaft centreline height must be 90mm +/-0.2mm. The engine bore size is fixed at 80mm.

"So nowhere here in this factory are we any more doing bore size investigations for conversion efficiency," says Cowell. "The challenges going forward are all about conversion efficiency. So it is about 100kg/h maximum fuel flow rate for 100kg of fuel, and about internal combustion engine conversion efficiency and energy management."

The lithium-ion battery systems from the existing Mercedes KERS provided the launch pad for the E-Cell battery packs. In 2010, work started on a new road car project. The first SLS AMG E-Cell prototype has the E-Cell designed by the engineers who in 2007 developed the first KERS system that was made, assembled and tested at Brixworth.

"We are now in the last stage of battery pack development," says Cowell.

Such packs, of which there are three, effectively replace engine, transmission and rear axle in a normal road car. They feed power into four AC synchronous wheel motors with a combined output of 392kW and maximum torque of 880Nm.

Each compact motor has a maximum speed of 12,000rpm and is positioned near to the wheels. This substantially reduces the unsprung mass compared to conventional wheel hub motors.

The gullwing can accelerate from zero to 100km/h in 4s--almost on a par with an SLS AMG powered by a 6.3-litre V8 engine giving 420kW, which takes 3.8s.

As in KERS, a high-performance electronic circuit converts DC from the high-voltage battery into AC and regulates the energy flow for all operating conditions. Two low-temperature cooling circuits ensure that motors and power electronics maintain operating temperature.

The three batteries require their own separate complex, low-temperature cooling systems using secret liquids still under development. The radiator is larger than for a passenger car. At low ambient temperatures, the batteries are brought up to operating temperature, while in hot weather cooling is boosted by air conditioning.

Total energy content is 48kWh and the rated capacity is 40Ah (at 400V); this can provide a range of 200km.

The choice of cells, of which there are 1,000, offered a "unique challenge" to the team as engineers bought and tested a large number of designs. It is believed that Mercedes is the only company using this type of cell. The present cell, the second design iteration, will be followed soon by a third iteration ready for production start-up in 2013. Each battery pack has its own control system.

Brixworth makes almost everything that is required for an F1 engine, with the exception of the gears, so every resource is available to help fill any loss of engine production when battery technology takes its meaningful place. For example, special teams are investigating new alloys.

The entire site is based on the ethos of quality, technical excellence, and speed and flexibility of operation. Underpinning quality are product assurance, process repeatability and continuous improvement that extends from planning and concept to manufacture and final test. Each and every F1 team receives the same service.

"It would be wonderful if lap times were to be the same as today's if the cars were emitting 35% less carbon dioxide," says Cowell.
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Title Annotation:AUTOMOTIVE
Author:Mortimer, John
Publication:Professional Engineering Magazine
Date:Jan 1, 2012
Words:1445
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