New tricks for an old technology

How does this sound: a hybrid BMW 530i that uses 52.7 per cent less fuel than a normal petrol 530i -- 6.58L/100km, down from 13.89 for the unmodified car.

That's what Scottish engineering firm Artemis Intelligent Power claims to have achieved in European test conditions with its prototype hydraulic hybrid drive system. Under nastier US conditions, the prototype achieved 30 per cent fuel consumption savings over its conventional equivalent.

All from technology that doesn't command a massive premium over conventional power plants.

Artemis's so-called digital displacement system integrates an infinitely variable transmission (IVT), a compact hydraulic pump and what Artemis calls an energy accumulator -- a gas- and hydraulic fluid-filled cylinder filled capable of storing and converting energy. The accumulator is connected to individual hydraulic motors for each of the drive wheels. It's equivalent to the battery pack in an electric hybrid, in that it's capable of storing and regenerating energy that would normally be wasted in braking.

When the car takes off, the energy goes back to the drive wheels via the hydraulic wheel motors. Since getting off the mark is the area in which the burner uses most of its energy, the system dramatically reduces the aggregate demands placed on it, thereby also reducing fuel consumption and exhaust emissions. A hydraulic starter motor gives the system gives the system an auto stop/start capability more effective than its electric counterparts, says Artemis, because hydraulics serve up more kick to start the engine much faster.

This means during braking and stop time, the engine can be switched off completely. Pressing the accelerator releases energy from the accumulator to the drive wheels and the starter to get the engine going again. While the engine's off, the pump motor drives auxiliary power drains like the alternator, pumps and power steering as it recharges the accumulator.

Artemis claims advantages to the system on a number of levels. With the IVT directing the engine to optimal revs constantly and quickly, it extracts 2.0-litre performance from a 1.6-litre engine, with better fuel efficiency into the bargain. In cruising, it's capable of pushing the engine up into long-legged overdrive ratios faster than conventional fixed ratio boxes, and with none of the energy dissipation problems suffered during conventional incremental upshifts. And it allows very quick kickdown shifts from very high overdrive ratios, meaning higher top speed, better fuel consumption and lower emissions with no sacrifice in overtaking power.

The hydraulic accumulator generates the same kind of city cycle operating efficiencies as can be expected from any electric hybrid. More so with the addition of the stop/start function.

The use of independent hydraulic wheel motors mean RWD and AWD cars can dispense with conventional drive shafts and the interior floor humps they create. The motors are compact enough to make it easy to set the system up for FWD, RWD or AWD. It also makes the system amenable to sophisticated traction control systems.

"A lot of people have played with hydraulics for car and trucks, but conventional hydraulics are very inefficient at part-load, when, for example, a car is cruising down the motorway. You can have perfectly good transmission, but if it is not effective at 20 per cent of full power it is a non-starter. What our technology brings is the ability to be efficient at 10 or 20 per cent of full power," said Waverley Cameron of Artemis Intelligent Power.