Smart Fortwo Micro Hybrid Drive (MHD) has been available for quite a while on Europe’s car markets. It’s Smart’s way of saying “I am cleaner than the cleanest”, and a quite impressive innovation that brings some kind of a “hybrid” system into play by using a start-stop mechanism of the engine. It uses regenerative brakes, like all hybrids do, to recharge the battery, and it stops the engine when you halt at a stop light (in fact, when your speed drops below 8km/h).
When you do push the pedal, though, it is not responding instantly, but hesitates a second until the computer starts the engine. It is a very quick start, and the regenerative brakes seem to keep up with charging the battery for the next engine start. Without those fancy regenerative brakes, the battery would deplete before you reached home.
Mercedes Benz also implemented such a start-stop system on their BlueEfficiency line. The difference
between those bigger hybrid brothers and Smart is that Mercedes have both a belt-driven starter generator and a conventional classic starter motor for cold starts, and Smart has both implemented in a starter generator, so the design is smaller and more simple (and the belt breaking rate is probably bigger).
About the fuel efficiency and saving, Smart reckons the MHD system improves fuel economy by 8 percent in mixed conditions and up to 13 percent in urban driving. That’s a lot, considering that there is no battery to charge, nothing heavier than the usual Smart, but everything is kept to a minimum, and with a slight difference in engine control you get extra mileage.
Pretty neat invention!