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Generators with high-efficiency diodes and synchronous active rectification


Bosch generators with high-efficiency diodes (HEDs) and synchronous active rectification (SAR) have now been officially recognized by the EU as fuel economy innovations. These components make vehicles more efficient and more economical, so they are able to meet the European Commission’s strict CO2 targets. European regulations set an average emissions limit of 95 grams of CO2 per kilometer for new vehicles starting in 2021. That equates to fuel consumption of just over 4 liters per 100 kilometers. In 2013, average CO2 emissions from new vehicles were still 132.9 grams per kilometer.

With the “eco-innovation” label, the EU recognizes particularly eco-friendly technologies. Vehicle manufacturers can have these technologies count as CO2 credits toward calculating their fleet fuel economy figures. The maximum permissible credit is seven grams per kilometer. Bosch is offering three EU-recognized eco-innovations: a navigation-based battery management system for hybrid vehicles plus the two new generator technologies.

“Bosch is improving every aspect of the internal-combustion engine,” says Dr. Rolf Bulander, member of the board of management of Robert Bosch GmbH. The new generators are a case in point: thanks to their excellent efficiency, the HED and SAR generators alone reduce CO2 emissions by one to two grams. At the same time, they provide more electrical power than standard generators when starting and at low engine speeds.

High efficiency generators reduces emissions

Generators are the power stations on board every vehicle. They reliably provide power to the safety, convenience, assistance, and injection systems as well as to engine management. They also recharge the car battery. To do this, generators convert mechanical energy into electrical energy. The higher the generator’s efficiency, the lower the vehicle’s fuel consumption and hence its CO2 emissions. To increase the efficiency, Bosch engineers took a close look at numerous generator details and made improvements, especially in the area of losses arising from rectification of the alternating current generated.

Generators with high-efficiency diodes (HEDs) and synchronous active rectification (SAR)

The high-efficiency diodes developed in-house reduce the generator’s CO2 emissions by up to 1.3 grams per kilometer. In addition, compared to standard generators, this efficient version delivers five to seven amperes more at low engine speeds. That is particularly important, since on-board power consumers need a reliable power supply even at low revs. The generator with synchronous active rectification even offers some ten amperes more than normal generators, reducing CO2 emissions by up to two grams per kilometer. With this technology, the diodes are replaced by high-performance transistors. Both generator versions are more efficient and help make the vehicle more eco-friendly – something the EU has confirmed by recognizing them as eco-innovations.

Synchronous active rectification Bosch Generator
Source: Bosch
Romain’s opinion:
Many components (engine, aerodynamics, after treatment, tires …) can be further optimized to reach lower and lower CO2 emissions. How do you think OEMs establish the priority between these ways of reducing CO2? Using development cost vs CO2 gain ranking or simply working first on the solutions with highest gains?

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