Bosch common rail for passenger car/light duty – The first 20 years

Abstract

For a long time the image of the Diesel engine was seen as a fuel efficient, but noisy and phlegmatic power source for passenger cars. With the introduction of turbo charging this turned around the first time. A second big step was the cultivation of the direct injection combustion technology, as it once again added a significant fuel consumption reduction opportunity compared to the in-direct combustion systems of these days. With the injection of fuel directly into the combustion chamber the control of combustion was shifted away from air motion much more towards the injection itself. As in former times pre- or swirl chamber concepts defined the course of combustion, the shape of the injection rate became the dominant parameter of controlling the combustion process. These new requirements now defined the boundaries for the next generation of injection systems.

One of the important steps was the introduction of electronic controlled valves and software functions, which offered the opportunity to meter the fuel more precisely and drove the transformation of mechanical pumps into the first computer controlled devices. Another important topic was the need of higher injection pressure levels to serve the combustion process requirements with less support of swirl or squish. Last but not least the control of combustion required a higher degree of freedom in terms of injection timing and pressure level within the whole engine map of the engine.

By stepping into this new exciting world of direct combustion the focus areas of combustion system developers at the OEM differed tremendously. As a result the requirements led Bosch to develop different injection systems serving all the new engine concepts. Therefore the start of passenger car Common Rail fuel injection technology is time wise strongly linked to the development of unit pump systems and different types of distributor pumps with a radial and axial plunger concepts. As this was an open race of technologies at the beginning, it is a must mentioning them as technical competitors of the early times of Common Rail.

The content of the presentation will focus on the technical development steps of Common Rail injector, as it was and is today the interface to the combustion and therefore direct link to the engine performance being the subject of biggest changes from a spring controlled nozzle holder to a sophisticated high precision mechatronic component. Nevertheless it has to be underlined, that all components, a Common Rail fuel injection system is containing of, went through significant development steps contributing to the all over improvement of performance during the last 20 years [1].