Technology developed for future hybrid vehicles has been adapted by Visteon to improve fuel economy and reduce emissions during town driving.
The SpeedStart 12 uses an integrated starter-generator (ISG) to shut down the engine when the vehicle is stationary and quickly restart it when the driver’s foot moves from brake to accelerator.
There is a claimed five per cent improvement in economy and carbon dioxide emissions over and above the new European Drive Cycle requirements, the test programme from which official mpg figures are derived. This saving is even bigger in long periods of town driving and will be seized upon by manufacturers struggling to meet European regulatory commitments. Car makers have signed up to a CO2 emissions target of 140g/km, or 49mpg, by 2008.
SpeedStart, which had been tested on a Ford Mondeo, achieves this improvement by eliminating idling in stationary traffic and improving generating efficiency.
Stop-start systems have been tried in the past, notably by Volkswagen, but with a conventional alternator and starter motor driveability was poor because it took too long to restart the engine.
It had been thought that it would be impossible to achieve reasonable levels of driveability in hybrid vehicles until 42V electrical systems were adopted. Visteon has achieved a start-up time of only 400m/secs, which is almost imperceptible. It sees SpeedStart 12 as bridging the gap until the arrival of 42V systems at the end of this decade.
The SpeedStart ISG uses a switched reluctance electric motor. This is a brushless motor offering better efficiency and more torque than a design-based on a conventional alternator. In hybrid systems such as that being developed for vans by Imperial College and Iveco or Honda’s Integrated Motor Assist, the integrated motor-generator is also used as a source of motive power and it is normally mounted in line with the crankshaft. SpeedStart 12’s ISG is belt-driven for reasons of cost and packaging flexibility, and is easy to fit to existing vehicles.
Miniaturised control electronics fit into a package of a similar size to a normal alternator. This is connected to the cooling system to maintain a stable temperature.Visteon worked with a specialist to develop the belt system. ‘We’re confident we can produce a system for any application,’ said Mike Dowsett, Visteon advanced powertrain systems manager.
The system’s other key component is a high-performance lead acid battery developed for marine applications and capable of deep discharge and fast recovery.
Electronics monitor battery condition and override the engine cut-out if the battery is in danger of becoming too discharged.
Improved generating capacity and 20 per cent greater efficiency compared with an alternator will allow manufacturers to add more features, according to Visteon. ‘The power limit of an alternator is about 2kW,’ said Dowsett. ‘They will run out of power in around 2006.’
Visteon believes the add-on cost of the SpeedStart system is about E150 (£103). It could be introduced by 2005-6 and is likely to find favour in family and executive models. It can crank petrol engines up to a 3-litre V6 at temperatures as low as -30 degrees C.
Diesels might need to retain a starter motor to cope with low temperatures, but the emissions benefits are potentially greater.