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smart set to roll out a full complement of Alternative Drive Systems

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July 9, 2007

smart set to roll out a full complement of Alternative Drive Systems

smart set to roll out a full complement of Alternative Drive Systems

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July 10, 2007 Mercedes-owned smart is set to become the first mainstream production vehicle with a full complement of alternative drive systems. It has begun touting four new versions of the smart fortwo, all of which can be expected in production form before the year is out. We’re not sure which is the most exciting as they all offer different solutions depending on your needs. The cleanest of the new smarts is the 30 kW plug-in electric version with a range of 115 kilometres (EUDC), but there’s also a 100 mpg 53 kW diesel hybrid drive, a slightly less economical petrol hybrid for those who don’t want diesel, a 52 kW micro hybrid petrol variant and a diesel-engined fortwo which will become the world’s most economical combustion-engined production car with 85 mpg (3.3 litres of fuel per 100 kilometres - NEDC) and the ability to travel 1000 kilometres without refuelling. The smart fortwo diesel is the world champion in low CO2 emissions at just 88 grams of CO2 per kilometre. This is huge news.

The smart fortwo electric drive (ed) - zero emission town and city car

It comes with everything that makes a smart a smart – but it doesn't have a combustion engine. A 30 kW magnetic motor runs at the rear of the smart fortwo electric drive that is driven by a high-performance, high-temperature battery made from environmentally-compatible sodium-nickel-chloride. This is housed in the underbody, which means that the interior space is not compromised.

Boasting New European Driving Cycle (NEDC) consumption of just 12 kilowatt hours per 100 kilometres and zero carbon dioxide emissions, the smart fortwo electric drive is the most economical and climate-friendly alternative in urban traffic. When charged, the 30 kW two-door car can travel around 115 kilometres (EUDC). When the battery is empty, it can be charged at any 230 volt power socket – at least 1000 times. The battery lasts for up to ten years. It takes four hours to charge it to 80 percent capacity and eight hours to charge it to full capacity.

The NEDC consumption costs stand at around just € 0.02 per kilometre, far below those of a combustion engine – despite offering almost the same performance. Acceleration from zero to 60 km/h is similar to that of the petrol variants and the car has a maximum speed of 112 km/h. Furthermore, as a zero emission car the smart fortwo electric drive enjoys tax advantages in many countries and is exempt from local restrictions such as the London congestion charge. This small electric car offers a combination of agility, economy and environmental compatibility that is unique in this class.

The smart fortwo hybrid drive (hd)

The combination of an electric motor and a combustion engine makes the smart fortwo even more economical and environmentally friendly than ever. The hybrid concept reduces consumption and emissions for both the diesel and the petrol version by around 12 percent. For example, the standard consumption (NEDC) of the smart fortwo hybrid drive diesel is reduced from 3.3 litres to 2.9 litres per 100 kilometres. Carbon dioxide emissions fall from 88 to 77 grams per kilometre. This means that the CO2 champion is setting new standards for the "three litre" car class. No other diesel car is more fuel-efficient and climate-friendly.

The smart fortwo hybrid drive has a 33 kW combustion engine and a 20 kW electric motor that is driven by a nickel hybrid battery (1 kWh). Both motors can work together or separately.

The exclusive use of the electric motor enables fuel-saving and completely emission-free driving in urban traffic i.e. zero emissions and no noise. The combined use of both motors provides for a considerable increase in power and torque. In figures, this means that the combustion engine delivers power of 33 kW and maximum torque of 110 Newton metres, whilst the electric motor has power of 20 kW and maximum torque of 50 Newton metres. Together, these add up to an exceptional 53 kW power pack. The torque interruptions when changing gear, especially when changing from first to second gear, are compensated by simultaneous use of both drives. This enables the smart fortwo hybrid drive to accelerate from zero to 100 km/h approximately four seconds faster than the smart fortwo cdi. In this way, the hybrid concept offers a unique combination of driving fun, economy and environmental friendliness.

All new components have been integrated in the existing smart cable harness and databus architecture. The electric motor is connected to the axle drive. The battery is housed under the driver's seat and is charged via the motor and by recuperation of the braking energy. This means that the hybrid drive is a fully independent system.

The smart fortwo micro hybrid drive (mhd)

From 15 October 2007 a particularly economical 52 kW variant of the smart fortwo with a start/stop function will roll off the production line in Hambach, France: the smart fortwo micro hybrid drive. From the end of the year it will be available as a coupé and a cabrio in all three lines – "pure", "pulse" and "passion". In addition, a limited special series that will offer an attractive price saving is planned to mark the market launch. The micro-hybrid variant will be available as a left-hand-drive ECE version in Germany along with other markets.

The smart fortwo micro hybrid drive uses idling phases to switch off the engine and temporarily completely avoid fuel consumption, exhaust gas and noise emissions. In combination with the automated manual transmission already fitted in the production vehicle, customers can comfortably use this function with maximum start/stop availability. Studies have shown that in everyday traffic vehicles come to a stop every 1.3 kilometres on average.

At the heart of the system is a special belt-driven starter generator that supplies the vehicle's electrical system with voltage and has a secondary function as a starter. It is able to smoothly start up the combustion engine in a fraction of a second as soon as the driver releases the brake pedal. This dispenses with the need for a conventional starter motor that works on the flywheel of the crank assembly.

In conjunction with slightly modified gear ratios, this strategy leads to a fuel saving of approximately 8 percent in the New European Driving Cycle (NEDC). The standard consumption is reduced by approximately 0.4 litres per 100 kilometres – from 4.7 litres to around 4.3 litres. Depending on the traffic situation (heavy slow traffic), this can lead to a fuel saving of approximately 13 percent.

There is also a corresponding reduction in CO2 emissions from 112 grams to approximately 103 grams per kilometre.

The system was developed by smart in cooperation with Valeo GmbH and the Gates Corporation. The mechanical assembly comprises the starter generator STARS 137 from Valeo. This generator delivers torque of 42 Newton metres or current of maximum 120 ampere at 14 volts – enough to guarantee a reliable engine start, even at a temperature of minus 25 degrees Celsius. To ensure a low-slip and durable connection of the crank assembly and the starter generator, both components were given wider belt pulleys, as was the water pump that is also driven. A six-rib poly-V-belt from Gates transmits the power.

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 battery stores the energy for the on-board electrics. The electrolyte is bound in an absorbent glass matt. 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 in idling phases, for example at traffic lights or in stop-and-go traffic. In view of fuel economy and comfort, the electronics switch off the engine at a speed of below 8 km/h when the driver presses the brake pedal, signaling that he or she wants to 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 centre console – until the next starting procedure (ignition off/ignition on).

The new smart fortwo cdi

With the development of the world's smallest direct-injection diesel engine, smart has produced a masterpiece of engine development that earns the new smart fortwo cdi the distinction of the world's most economical production car with combustion drive. The 33 kW two-door car consumes just 3.3 litres of fuel per 100 kilometres (NEDC), which means that it can travel approximately 1000 kilometres without refuelling. Emitting just 88 grams of CO2 per kilometre, the smart fortwo diesel is the world champion in low CO2 emissions.

State-of-the-art common-rail direct injection enables a combustion process that is even more efficient than that of the well-proven cdi engine from the predecessor model. High injection pressure of up to 1600 bar (previously 1350 bar) is built up, even at low revs, and the fuel is injected into the combustion chambers with newly developed seven-hole injectors.

Power and torque have each improved by 10 percent. At the same time, fuel consumption is reduced by 13 percent. Depending on the driving situation and engine load, up to 60 percent of the previously cooled exhaust gases are returned to the combustion chambers.

Like the CDI engines of its sister brand Mercedes-Benz, fuel injection in the smart fortwo cdi is carried out in two phases: a few milliseconds before the main injection a small quantity of diesel is injected into the combustion chambers where it ignites and preheats the cylinders. This results in a noticeably quieter combustion noise level than an engine without this pilot injection. The electronic "brain" of the cdi engine – a high-performance micro-computer that controls the whole engine system – calculates how much fuel is needed and the interval at which pilot injection and main injection take place.

The quick response of the cdi engine is first and foremost thanks to the compact yet extremely effective turbocharger that is housed in the exhaust manifold. Its compressor wheel has a diameter of just 33 millimetres, yet it rotates at up to 280,000 rpm and thus builds up maximum charge pressure of approximately 1200 millibars. This gives the three-cylinder engine more air to "breathe" and enables it to develop impressive torque, even at low revs: 85 Newton metres are available even from 1500 rpm – more than three quarters of the maximum torque.

This torque curve plays an important part in the fun behind the wheel that drivers experience with every kilometre driven in a smart fortwo cdi. The new smart fortwo cdi accelerates from zero to 100 km/h in 19.8 seconds and reaches a top speed of 135 km/h. It therefore offers a combination of agility, economy and environmental compatibility that is unique in this class.

For more technical data on the new smart range visit the image gallery.

About the Author
Noel McKeegan After a misspent youth at law school, Noel began to dabble in tech research, writing and things with wheels that go fast. This bus dropped him at the door of a freshly sprouted Gizmag.com in 2002. He has been Gizmag's Editor-in-Chief since 2007.   All articles by Noel McKeegan
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