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smart Micro-Hybrid Going Into Production

smart fortwo mhd.

With the weekend’s Live Earth concerts as a backdrop, smart announced that it will begin production of a micro-hybrid variant of the smart fortwo. (Earlier post.) The smart micro-hybrid will be available as a coupé and a cabrio in all three lines: pure, pulse and passion.

The 52 kW (70 hp) smart fortwo micro-hybrid drive (mhd) uses a belt-driven starter generator from Valeo (StARS 137) to provide stop-start functionality. To ensure a low-slip and durable connection of the crank assembly and the starter generator, both components have been given wider belt pulleys, as was the water pump. A six-rib poly-V-belt from Gates Corporation transmits the power.

In conjunction with slightly modified gear ratios, the micro-hybrid system provides a fuel saving of approximately 8% in the New European Driving Cycle (NEDC). Standard fuel consumption of the 1.0-liter gasoline engine is reduced by approximately 0.4 liters per 100 kilometers—from 4.7 liters to around 4.3 liters (54.7 mpg US).

Depending on traffic conditions, this can lead to a fuel saving of approximately 13%. There is also a corresponding reduction in CO2 emissions from 112 grams to approximately 103 g/km.

Belt tension is particularly important because of the changing loads in start/stop operation. A coaxial spring-and-shock absorber unit that is hinged to the starter generator is supported by the engine block. The starter generator is pivoted so that it can apply the tension force to the belt drive. This ensures that both the belt section pulled by the combustion engine when it is running and the complementary belt section pulled by the starter during the start are able to reliably transmit the torque needed.

The activities of the system are controlled by a separate control unit with integrated power electronics that is installed behind the battery recess. This communicates with the vehicle’s other control units via CAN databus. A three-phase cable transmits the generator power of up to 120 ampere. The power electronics regulate the power of both the starter and the generator.

An AGM lead-acid battery stores the energy for the on-board electrics. Its physical properties make it more resistant to varying loaded and unloaded conditions (more cycle resistant) than conventional lead-acid batteries with sulphuric acid electrolyte.

The power electronics of the belt-driven starter generator switch off the combustion engine at a speed of below 8 km/h when the driver presses the brake pedal, signaling a stop. The engine starts as soon as the driver releases the brake pedal again. This guarantees an immediate response. The start/stop function can be deactivated if required with a switch on the center console until the next starting procedure (ignition off/ignition on).

smart also showed an all-electric version of the fortwo. A 30 kW/40 hp magnetic motor runs at the rear of the smart fortwo electric drive that is powered by a Zebra sodium-nickel-chloride battery housed in the underbody.

NEDC power consumption is 12 kWh per 100 kilometers. When charged, the 30 kW/41 bhp two-door car can travel around 115 kilometers (72 miles). An 80% charge takes four hours at a 230-volt outlet; a full charge takes 8 hours. The battery has a cycle life of at least 1,000, and lasts for up to 10 years.

smart created the electric drive in cooperation with Zytek, a British company that focuses on developing hybrid and electric drives. (Earlier post.) The company currently has the smart ev in a commercial trial for the UK market. (Earlier post.)

(A hat-tip to Mark!)


and when will be able to buy the pure electric version at a reasonable price!


The electric drive is cool. But the micro-hybrid is some sort of Rube Goldberg contraption. Belts? Lead-Acid? Come on! I'd guess they are still using low-voltage (prob. 24 or 36V) too. With that defeat switch, I'd bet over half the people decide the start-stop is too jerky and just let the engine run.

What's called for right now is a little innovation and technological leapfrogging, not crap implementations of 20 y.o. tech.

I suppose a micro-hybrid is better than nothing, but not by much.


For those of you who, like myself, may have forgotten what a Rube Goldberg Machine is: It's a very complex machine made to perform a very simple task:

Bud Johns

I would imagine the defeat switch is for when you are in heavy traffic, constantly stopping and creeping forward. My Prius has no such problem,as it just creeps forward under electric power. I wonder what it's like in the civic hybrid?


Pardon! Why is it called hybrid? It´s just a modern starter-generator for the engine and electric systems (should be used in every car).
There is no electric motor to propell the car! They combined just generator and starter motor into one system.

Mercedes is just abusing a technical term, developed by Japanese car makers.

German car makers do not offer any hybrid car now!

Define Hybrid:

Somebody should define the minimum requirements to justify the (elctric) HYBRID name.

Hybrids should have a certain degree of electric propulsion or electric assisted propulsion.

Vehicles with stop-start gadget are NOT hybrids.

Multi-fuel ICE vehicles are NOT hybrids.

More proposals?

DRD T-bone

The use of the word hybrid is just an attention getter to signify some use of electronics to improve fuel economy at this point. There's no reason in arguing over naming semantics, it gets in the way of focusing on the results that these small improvements achieve. 103 g/km is nothing to scoff at.

Charles S

I agree that the term "hybrid" has lost its meaning a long time ago. The worse part is that there are still (probably many) people who have no idea what a hybrid is, or how it works. People still ask us if we have to plug in the car at night. If you try to explain to them, their eyes just glaze over.

In my fantasy world, I'd hope that people will take the time to do research and be informed before they buy or bash a hybrid, but in reality, "hybrid" will just be the buzz word to hook the clueless.

John L.

I'm not sure whether to be pleased or disappointed.

Our family's primary car is a Prius. Under real-world conditions, we get about 46 MPG in this car. (I can get 52 MPG -- my wife has a heavy foot, and we try not to talk about it...)

Our second car is a 1994 Honda Civic. I've been thinking that, when it dies, I'd like to be able to replace it with a hybrid two-seater. With the Honda Insight out of production, I've been looking for an alternative. It even occurred to me that the Fortwo would be a good chassis on which to base a new hybrid two-seater.

Now a hybrid Fortwo has been announced. But it only gets eight percent better gas mileage than the conventional model? And, tiny as it is, it's barely more efficient than the Prius? What's up with that?

My uncle owns a manual-transmission Insight and he regularly achieves 65 MPG, real-world.


The electric vehicle seems interesting. The "hybrid" is just abuse of the term. It would be great to see Smart develop a proper hybrid version of the Smart and even better a plug in hybrid.

John L: Does your wife do shorter journeys on a cold engine?

Michael McMillan

Notice that the press release doesn't say the size of the battery pack? Though the pack needs to be at least 15 KWH to supply 30kw to the motor (maximum 2C).

Zebra packs also loose power through thermal loss (they must be hot to be used, like 350C). For heavy in city use, this is great, but for occasional use, you may loose more power through thermal loss than you will save by going electric. Though the pack will last a long time, as they usually get in excess of 2000-3000 cycles, and 8000 cycles is not unheard of.


John L.

John L: Does your wife do shorter journeys on a cold engine?

Posted by: Alex | Jul 12, 2007 4:01:54 PM

Alex: No, she tends to take the longer journeys.

She has a heavier foot than I have. She tends to anticipate traffic less than I do -- to the point that she says "watch out!" frequently as I'm driving and closing in on a car ahead of us. She thinks I haven't seen the car, but in fact my foot has usually been off the accelerator for several seconds and sometimes I'm already applying the brake. Prius brakes are wonderfully gentle that way.

She also cranks the air conditioner to "max cold" when she wants 72 degrees, and she cranks the heater to 74 when she wants 70.

In a nutshell, that's why we try not to talk about gas mileage. :^)


Actually it probably doesn't get better average gas mileage than the Prius. Remember you are measuring actual real world gas milage while they are using the standard tests.

Still ... as others have commented ... its certainly nothing to scoff at.


I drive a 2003 Civic Hybrid..regards the question about what is the civic like in heavy traffic...Once you stop the first time and then start and creep forward the engine stays on UNLESS you creep forward at more than 10+ MPH. Then the Auto Stop feature will re-engage. It's very seemless, however here in Dallas in the summer it's freakin HOT and HUMID and I have a tendency to turn the ECON mode off and let the engine run and provide A/C. Still over the course of a hot summer I still get 43MPG.


15kwh sounds about right based on the listed range of the EV version too. Anyone know how much a 15kwh zebra costs? The same in LiFePO4 would be 12K US approx.


Neil ,
mass production price should be around 200 euros per kwH , however
the shortage of manufacturers seem to be keeping the price artifically high
at the moment .
I had a drive of a Zebra powered Panda a couple of months ago , really
quick , and quiet none of that of that small car thrash just a low whine ,It
will never reach serious prodution ,just too good !

Joe E Shotwell

I want to know when I can place an order.

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