Bosch suggests cars to coast for better fuel efficiency

December 11, 2013 // By Christoph Hammerschmidt
With a package of relatively simple but coordinated measures, cars can raise their fuel efficiency. Automotive supplier Bosch claims that the technique can be applied to almost any vehicle design; even existing ones can be modified without much effort.

Bosch's measures involve in the first place syntonic modifications of the software at several places in the vehicle, such as engine control or transmission control. In the case of manual transmissions, the clutch has to be exchanged against Bosch's eClutch, an electronic clutch that separates the engine from the powertrain under no-load conditions. Under such conditions, the software then switches the engine off, the car can coast over significant distances without burning fuel and without generating exhaust gases. As soon as the driver hits the throttle, the engine is automatically re-started and generates thrust.

Bosch conducted tests which showed that during about 30% of the driving time, the engine power is not needed at all. Thus, vehicles could actually coast over almost one third of the distances. The standard test procedure to measure fuel consumption, the New European Driving Cycle (NEDC), does not take this driving mode into account. However, in practice drivers can expect fuel savings of up to ten percent, the company claims.

The function is widely based on software enhancements. Beyond this, the vehicle to be equipped accordingly requires a start/stop motor designed for higher use and a faster restart than conventional vehicles. The effort is relatively low and can be integrated into almost any existing powertrain design, be it a European diesel, an American gasoline engine or an Asian natural-gas drive.

In some vehicles, coasting is already possible with existing vehicles: Double clutches automatically switch to idle as soon as the driver takes his foot off the pedal. In this operating mode, the vehicles coasts along, but it still burns a certain amount of fuel since the engine is still idling. Bosch's approach utilizes start/stop systems where the engine is turned off completely as soon as the vehicles stops - for instance at a traffic light. This concept is already implemented in mild and micro hybrid powertrains. Bosch now goes one step further and turns off