'Performance' Hybrids are not the answer

Dr Andreas Truckenbrodt, Mercedes-Benz parent company Daimler AG's executive director of hybrid development, is in Australia to present a three-axis strategy for Mercedes-Benz's future model range: Conventional/alternative fuels, battery/electric and fuel cell -- as means of storing energy.

During a rehearsal for his part at the annual Banksia Foundation Forum environmental awards, he told journalists that 'performance' hybrids were not the way forward for manufacturers.

Using the Lexus LS600hL as an example, Truckenbrodt pointed out that the battery bank for the Big L (pictured) occupied so much boot space that it was effectively a Pyrrhic victory of 'can do' over common sense.

In discussing options for placement of a larger battery pack, Truckenbrodt said: "We don't know really where to put it in the vehicle, other than getting rid of the spare tyre -- that's what we're doing at the moment. We do not want to do it like Toyota does it. If you have seen, in Australia, the LS600... There is no comfort left."

Nor are capacitors any help, says Truckenbrodt. [Capacitors can store large reserves of energy for short periods and could supplement smaller battery packs to provide a burst of power when needed. They've already been adopted in a Toyota Supra hybrid prototype raced in Japan.]

Says Truckenbrodt: "It would be an option, but then capacitors are unfortunately as critical as batteries, in terms of development maturity.

“The other issue is the system is very, very complex. You still need a battery for long-term storage, so you would then have to deal with two energy storage systems, which complicates things an awful lot. And my battery folks tell me that you could do kind of the same with a battery that you can do with capacitors -- from a cost and efficiency point of view."

Truckenbrodt provided evidence for his point of view, in the form of the Mercedes-Benz F 700 (pictured). The S-Class-sized hybrid concept was revealed at the Frankfurt Motor Show with a 1.8-litre 'DiesOtto' engine coupled to a 'frugal' electric drive system. It returns a fuel economy figure of 5.3lt/100km and yet produces power of 175kW from the combustion engine and 15kW from the electric motor -- enough to maintain speed and provide some torque when needed, though without crippling the car with the added weight of a massive battery pack for performance motoring.

Truckenbrodt's argument goes like this, the same energy stored in a litre of petrol would need a battery pack occupying 22 litres of volume.

Thus it's a case of dwindling returns. The more power you expect from electric motors and batteries (with the limitations of current battery technology), the more this impinges on packaging and weight. More weight reduces the efficiency gains of a hybrid vehicle.

In other words, hybrids have their place in a fuel-sipping scenario, but Truckenbrodt tells us that the fuel economy advantages enjoyed by the Lexus could be achieved by optimising combustion engines just as readily as bunging in two 165kW electric motors and the battery bank to go with them.