Bosch has developed a new start-stop system with coasting mode; the system stops the engine when the vehicle is traveling at speed, helping to reduce fuel consumption by up to 10%. The function can be combined with any type of combustion engine.
First generation start-stop systems stop an engine only when the vehicle is completely stationary; enhanced versions of this start-stop system cut the engine as soon as the vehicle is coasting to a halt—e.g., at a red light. In contrast, as soon as the driver’s foot is off both the gas and the brake pedal, vehicles equipped with the new start-stop coasting function stop the engine while the vehicle is in motion. Because the engine is disengaged, the vehicle can coast for longer than it could with an overrun fuel cutoff system, for example.
Whenever the vehicle can maintain its speed simply by rolling—for example, on a gentle incline—the engine is stopped. As soon as the driver touches the gas or brake pedal, the engine starts up again. Tests carried out by Bosch have shown that the combustion engines runs needlessly about 30% of the time, meaning that the vehicle could simply coast for about a third of every journey.
Although these phases are not taken into account in the New European Driving Cycle (NEDC), under real traffic conditions the function will give drivers a roughly 10% fuel saving.
Much of what enables the system innovative is its enhanced software and the use this makes of existing sensor data. Furthermore, the start-stop starter has been configured to cope with greater loads and to deliver faster restarts.
With double-clutch transmissions, Bosch noted, 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.
Bosch is confident that start-stop coasting will soon become an everyday feature in cars—just like air conditioning.—Dr. Rolf Bulander, member of the board of management of Robert Bosch GmbH
Bosch is embedding fuel-saving functionality in many of its products. One example is eClutch, which makes it possible to offer the coasting function even in vehicles with manual transmissions. As soon as a coasting phase is possible, eClutch decouples automatically and the engine is stopped.
The coasting function is also available as an add-on for the Bosch entry-level hybrid, the boost recuperation system, to help it save even more fuel. Equipped with a more powerful generator and a compact lithium-ion battery, the 48-volt hybrid saves around 15% 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 an additional 10%, or 25% overall.