As powertrain engineers seek constant improvements in engine efficiency, often through downsizing and boosting, they are exposing the limitations of existing turbocharging and supercharging technologies. Matthew Beecham spoke to Bryn Richards, CEO of UK-based Aeristech, about the latest developments in this area and what they could mean for future vehicles.

Electric supercharging has been promoted for some time as a lag-free alternative to turbocharging. Why hasn't it caught on as yet?

There are two basic limitations; the power available and the duration of boost. A 12v system is severely power limited and only really capable of providing infill torque at low engine speeds during brief transients. This gives some benefit to the driveability of a downsized engine but still relies on the turbocharger to provide the steady-state boost at all engine speeds, which becomes increasingly difficult as boost levels increase.

Independent experts such as AVL predict a rapid growth in the popularity of 48v systems during the next ten years. These will enable an electric supercharger to make a more useful contribution, but the duration of boost will still be restricted by cooling challenges because of limitations in switched reluctance electric motor technology.

What's so special about the Aeristech alternative? What have you done differently?

Our solution is the first eSupercharger capable of sustained operation at useful power levels, by using advanced permanent magnet motor technology to overcome the thermal management issues related to switched reluctance motors. We have developed unprecedented levels of efficiency (over 95 percent) for both the electric motor and controller through a combination of patented motor control architecture and permanent magnet technology. By separating commutation from power control, we are able to use a very low electrical switching frequency that allows us to use cost-effective IGBT/MOSFET components.

The low mass, permanent magnet e-motor provides high efficiency and torque density with exceptionally accurate motor control during extreme transients, providing rapid acceleration and operating at up to 150,000 rpm with a transient response of idle to target speed in <400ms.

Is this all in the future? How far have you progressed the technology?

Our 48v eSupercharger has already been demonstrated by Mahle in a D-segment appraisal vehicle using the Mahle downsized 1.2 litre, 3-cylinder gasoline engine. The engine achieved 33 Bar BMEP at 2000rpm and an astonishing 313Nm and a maximum power output of 193kW. The peak power consumption of the eSupercharger system including the losses from the power electronics, under steady state conditions, is less than 7 kW.

We will be launching the technology to a wider audience during this year through licensing arrangements with interested parties. We have effectively become a 'one-stop shop' for all technologies related to electric forced induction, including high speed bearings, motors and control electronics.

Can't a two-stage turbo achieve the same result?

The original Mahle engine used two-stage turbocharging but this was considered too costly for potential series production applications. The engine was reconfigured with a single stage turbocharger but Mahle wanted to achieve higher specific outputs that would permit more extreme downsizing and greater savings in CO2 emissions, so a new solution was required.

By adding an Aeristech 48v eSupercharger, Mahle was able to use a larger turbocharger, increasing the specific output. The detrimental effect on low speed torque and driveability that normally accompanies such a large turbo was completely alleviated by the eSupercharger and the torque output with the combined system exceeded that of the baseline engine at all speeds.

An eSupercharger is much easier to accommodate within the engine compartment than a second stage turbocharger because there is greater flexibility in the layout. It is applied to the inlet side of the engine, so it reduces the thermal mass in the exhaust stream which helps to maintain catalyst temperature, especially at lower speeds and loads.

Wouldn't a conventional supercharger have the same advantages?

Conventional belt-driven mechanical superchargers constantly consume some of the power the engine produces, unless connected through a clutch which can, in itself, introduce issues for the accessory drive when re-engaging. The rotational speed of a mechanical supercharger is a function of engine speed, which constrains the air delivery to increase with crank speed and may require the inefficient wasting of surplus air under some operating conditions.

Electric superchargers are decoupled from the engine so can be activated only when required. Energy recuperation during vehicle deceleration events has the potential to capture much of the electricity required to power the eSupercharger without consuming any additional fuel, depending upon the storage capacity of the 48 V battery and the nature of the vehicle duty cycle.

Mechanical decoupling of the supercharger from the engine sounds like a fundamental step. Does it open up new possibilities for the future?

The remainder of this interview is available on just-auto's QUBE Global light vehicle turbochargers market- forecasts to 2030