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

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.

...continued