Torqueing about a rev-olution

Automotive consultant Ricardo has unveiled an affordable ‘mild-hybrid’ system that promises impressive improvements in fuel economy and emissions.

The i-MoGen (intelligent motor generator), developed with French component supplier Valeo, would add less than £640 to a car, the firms claim. This would imply a hybrid Astra would cost around £14,000 compared with £17,000 for the Honda Insight, and the few hybrids already on the market.

Like the Visteon Torque Enhancement System, i-MoGen is built on the underlying philosophy of downsizing: extracting more power from a smaller engine without a fuel consumption penalty. But whereas the Visteon system uses an electric supercharger, i-MoGen has a combination of turbocharging and boost from an electric motor/generator. Ricardo says it could be introduced in evolutionary steps.

It was developed over 22 months in Ricardo’s biggest ever internal R&D programme, costing £4m. Valeo is thought to have invested another £2m.

The project took as its performance benchmark a Vauxhall Astra 2-litre TDi 16v diesel. It set a target for fuel consumption of less than 4litres/100km (over 70mpg), acceleration from 0 to 100km/h in under 12 seconds with good driveability and emissions of half the current Euro IV levels (estimated to be sufficient to meet requirements up to 2010). There was to be no compromise in refinement, seating, luggage capacity and handling.

The system combines five elements. The starting point is a diesel engine downsized to 1.2 litres, with more aggressive turbocharging to restore power to 100bhp. To restore torque at low revs and hence driveability, a 6kW, 42V electric Valeo motor/generator is mounted in line with the diesel’s flywheel. As well as boosting torque under acceleration up to 2,000rpm, this allows regenerative braking and, because it also replaces the starter motor, allows the engine to stop when the car is at rest in neutral, and instantly starts it again when first gear is engaged.

Engine management

In the only packaging compromise, 42V nickel-metal hydride batteries are mounted in the spare wheel well. Ancillaries such as the water pump and cooling and air-conditioning fans are run directly by Valeo 42V variable-speed electric motors, eliminating drive belts.

A new control system developed by Ricardo decides in which mode to use the motor/generator. ‘This takes engine management to a whole new level,’ said Ricardo technology department manager Nick Owen.

The car weighs about the same as the benchmark 2-litre model.

In-gear acceleration in top is faster. Fuel consumption is improved by 28 per cent: 20 per cent from the downsized engine, five from regenerative braking and three from the stop/start ability. The weight of the engine could be further reduced.

i-MoGen is a parallel hybrid (both the internal combustion or electric motor drive the wheels) and is similar in concept to the Honda Insight. It is cheaper because the Insight uses electrical boost across the whole rev range and hence needs considerably more batteries, and because the Insight also has a bespoke aluminium body. The Prius has a separate generator and motor and hence needs a more complex transmission system to take the drive from each to the wheels. But it can be used in full ‘zero-emission’ mode with the internal combustion engine stopped.

Ricardo and Valeo expect a significant market for mild-hybrid technology by 2010. Before then, says Valeo project director Michel Lifermann, ‘microhybrids’ with a belt-driven starter-alternator would help with economy, especially in petrol engines which have significant fuel consumption at idle. The next stage would be a high-efficiency alternator, still belt driven but using 42V electrics to provide significant boost, from 3kW to 8kW, and regenerative braking.

Test drive: David Fowler compares the I-MoGen hybrid Astra with the standard 2-litre diesel

The Astra is the typical mainstream modern diesel. There are none of the drawbacks associated with diesels of old, like a noisy idle: the lightly turbocharged unit is quiet and refined. With typical diesel low-down torque it pulls strongly from 1,500rpm, so you can leave it in third to negotiate roundabouts, for example. As the revs rise there’s no noticeable turbo lag.

This is the performance benchmark: can the I-mogen match it with just 1.2 litres?Outwardly, apart from the company logos, it looks like a standard Astra. Start it up, and the i-MoGen too pulls strongly from a standstill. The 1.2-litre engine maybe makes a bit more noise than the 2-litre at low revs, but it’s not intrusive. Acceleration from low revs is impressive.

Because this is a prototype, there’s a helpful Ricardo gauge that shows how much boost you’re getting. Another prototype-only feature is the ability to switch the boost on and off.

With the 1.2-litre diesel on its own, the car hardly wants to accelerate at all below 2,000rpm. Switch the boost back on and the car instantly feels livelier.

The electrical boost cuts out at 2,000 revs and there’s a hint of a flat spot till about 2,500, when the turbo really kicks in and the car feels, if anything, faster than the baseline vehicle. If they did it again, Ricardo engineers say they might have gone for a 1.4-litre engine and maybe an extra kilowatt or two of boost. But that possibly wouldn’t make the point so emphatically: this mild hybrid really does get 2-litre performance from a 1.2-litre engine, with much improved economy.

And it was developed in the UK. Shame it’s going to be so long before it hits the market.

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