The Smart Fortwo MHD has been available in Europe since October 2007. MHD is Smart-talk for a stop/start system and stands for Micro Hybrid Drive. UK versions of the 61bhp and 71bhp Smart will have MHD from October 2008, while the punchier 84bhp and Brabus models will have it in 2009.
Time for CAR to take one out for a traffic-jam test drive.
How does the Smart Fortwo’s MHD stop/start work?
Bigger stop/start systems like that in the A-class BlueEfficiency add a belt-driven starter-generator, but keep the conventional starter motor for cold starts. In the Smart, both the starter and alternator are replaced by the starter-generator.
The system generates electricity to charge the battery when the driver is braking, and automatically cuts the engine when the speed drops below 8km/h (about 5mph). It then re-starts the engine when the driver releases the brakes.
Click ‘Next’ to find out how the Smart Fortwo MHD drives
What’s the Smart Fortwo MHD like to drive?
In town, you soon get used to the rev-counter dropping to zero as you brake to a standstill: you’re rarely able to hear how silent the engine is because there’s usually a clattery diesel cab idling next to you.
The Smart’s semi-auto transmission stays in gear with the engine off, so when you release the brakes there’s just a moment’s hesitation as the engine is restarted and you’re away. You’ll really feel the hesitation if you stamp on the throttle from a standing start, but if you drive sensibly it’s hardly noticeable.
Does it make much difference to the MHD’s fuel consumption and emissions?
In town, yes. Smart reckons the MHD system improves fuel economy by 8 percent in mixed conditions and up to 13 percent in urban driving.
The regenerative braking pretty much cancels out the extra electrical energy needed to start the engine regularly in town traffic.
Click ‘Next’ for CAR’s first drive review verdict on the Smart Fortwo MHD
Verdict
MHD improves fuel economy and emissions, without compromising drivability. Unless you’re keen on traffic-light grands prix, that is – but then you wouldn’t be driving a Smart in the first place…
This tech just turns an already-clean car into an even cleaner one. It’s a neat solution.