Bosch suggests cars to coast for better fuel efficiency
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 the engine even during the ride as long as the driver does not have his foot on either the brake or the accelerator pedal, amplifying the fuel saving effect associated to microhybrids. To restart the engine, the starter engines pinion is engaged into the engine’s gear wheel, controlled by a smart algorithm that ensures a smooth start. In addition, the fuel injection control algorithm needs to be modified. Under certain circumstances, the engine deactivation can be controlled through the ignition control system without any mechanical action.
Under the Bosch concept, the engine brake is no longer available since the engine is disconnected. However, in some cases, for instance during downslope stretches, drivers prefer to rely on the engine brake for its mild, wear free means of retardation. They can do this also with Bosch’s approach: A short, soft kick on the brake pedal reconnects the clutch to the wheels and activates the engine brake, a spokesperson explained.
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