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Coasting with your car cuts fuel consumption

Published 2014-01-08

Bosch (Germany) has introduced the start-stop coasting function, which allows stopping the engine when the vehicle is traveling at speed. The automotive supplier expects to cut fuel consumption by 10 percent with this function.

The start-stop coasting system introduced by Bosch stops the engine not only in standstill but also when the car is in motion; whenever the vehicle can maintain its speed simply by rolling – for instance on a gentle incline – the engine is stopped (Photo: Bosch)

“START-STOP COASTING WILL BECOME AN EVERYDAY FEATURE in cars – just like air-conditioning,” stated Dr. Rolf Burlander, member of the board of management of Bosch. Tests carried out by the German car supplier have shown that combustion engines run needlessly about 30 percent of the time. Although these phases are not taken into account in the New European Driving Cycle (NEDC), under real traffic conditions the function will give drivers roughly 10 percent fuel saving.

The start-stop system with coasting mode is based on CAN-connected ECUs. The start-stop software running on these ECUs makes use of already existing sensor data. Furthermore, the start-stop starter has been configured to cope with greater loads and to deliver faster restarts.

In Germany, some three million new vehicles were sold in 2012. According to statistics, the annual average driven distance is around 11500 km. If every new car were equipped with the coasting system and emitted just ten grams less CO2 per kilometer as a result, the theoretical annual reduction in CO2 would amount to over 30000 t.

Due to double-clutch transmissions, some vehicles already have a “light” version of the coasting system on board. As soon as the drivers take their foot off the gas pedal, the system switches the engine to idle. While this means the vehicle is doing no more than rolling, it is still consuming fuel in order to keep the engine ticking over. With the start-stop coasting function, the engine stops as soon as the driver’s foot is off both the gas and the brake pedal.

The coasting function is also available as an add-on for the Bosch entry-level hybrid, the boost recuperation system. Equipped with a more powerful generator and a compact lithium-ion battery, the 48-V hybrid saves around 15 percent of fuel through electrification alone. In real traffic conditions, and fitted with the coasting function that shuts down the engine, the hybrid can achieve fuel savings of additional ten percent. The start-stop coasting function can operate with any combustion or hybrid engine.