Stop-start tech for Smart ForTwo
BY TERRY MARTIN | 3rd Nov 2008
Dubbed micro hybrid drive (MHD), the technology initially applies only to naturally-aspirated versions of the Mitsubishi-sourced 1.0-litre three-cylinder petrol engine powering the current second-generation ForTwo Coupe and Cabrio.
MHD replaces a conventional starter motor with a belt-driven generator that can act as a starter and also supply the electrical system with voltage.
Together with slightly modified gear ratios for the five-speed automated manual transmission, MHD enables the Coupe to realise a lower ADR 81/02 fuel consumption rating – down from 4.7L/100km to 4.4L/100km – and to achieve a corresponding reduction in CO2 emissions from 112g/km to 105g/km.
Both measures represent savings of about six per cent and are based on using the recommended premium-unleaded petrol.
Mercedes-Benz Australia/Pacific claims identical figures for the MHD Cabrio, which is slightly heavier and, in non-MHD form, adds 0.2L/100km and 4g/km over the Coupe.
Pricing for the MHD versions will hold firm at the current $19,990 for the Coupe and $22,990 for the Cabrio, with specifications also remaining unchanged.
The 999cc engine continues to produce 52kW at 5800rpm and 92Nm at 4500rpm, driving the rear wheels and accelerating from 0-100km/h in a claimed 13.3 seconds. Top speed remains at 145km/h.
Mercedes-Benz Australia/Pacific expects to make a similar running change with MHD to the 62kW/120Nm turbocharged version of the ForTwo Coupe and Cabrio in the first half of next year.
In its current form, the Smart EV produces 30kW and has a range of about 110km. A full recharge takes approximately eight hours. European trials recently incorporated new lithium-ion batteries, while small-series production of the electric two-seater is scheduled to commence at the end of next year.
“We haven’t got a final decision yet, but we’ve got our bid in for some and are pressing it strongly,” Mercedes-Benz Aust/Pac senior manager of corporate communications David McCarthy told GoAuto this week. “Because the first production is 1000 or so, they’re wanting to spread them around the markets.
But it does work in our favour that the (UK) trial was in right-hand drive.” The 33kW 800cc diesel version of the ForTwo available overseas, which enables fuel consumption and emissions as low as 3.4L/100km and a 88g/km, has also been on the Australian radar for the past 12 months.
“What mitigates against it is the relatively small production run they have to do for Australia,” Mr McCarthy said.
“Doing it in right-hand drive for our design rules and everything makes it expensive. Our allocation is limited in total Smart ForTwos... so adding another variant to that means we’d have less of the others.
“If I was asked whether we’d rather have the diesel or the electric, I’d say electric.” For the MHD petrol versions, the most significant savings – up to 13 per cent, according to Mercedes-Benz – will come in the urban environment where the (switchable) stop/start function comes into play.
MHD automatically switches the engine off when the vehicle’s speed is less than 8km/h and the brake pedal is applied. When the driver takes his or her foot off the brake, the engine will restart and first gear will be automatically engaged.
In describing the benefits of the technology, Mercedes quotes research showing that, on average, vehicles come to a stop every 1.3km in everyday traffic.
The MHD system was developed by Smart in co-operation with Valeo GmbH and the Gates Corporation.
The Valeo ‘Stars 137’ starter generator delivers torque of 42Nm or current of 14 volts (maximum) – enough to guarantee, according to Mercedes, a reliable start at temperatures as low as minus 25 degrees Celsius.
Read more:
Smart hits the USSmart ForTwo stays under $20K