BorgWarner Develops Two-stage Turbocharger for Mercedes-Benz Sprinter.

For 2006, the Mercedes-Benz Sprinter is using the benefits of two-stage regulated turbocharging (R2S) from BorgWarner Turbo & Emissions Systems for its new four-cylinder diesel engine. This innovative turbocharger

system allows an infinitely variable adaptation of the turbine and compressor side to any engine operating point.
The new 2.2-liter four-cylinder engine replaces the previous 2.7-liter unit. Due to the introduction of even stricter emission requirements in the future, the aim was to develop an engine that complies with these standards while maintaining almost the same nominal output and offering improved torque characteristics. The powerful new four-cylinder unit has a rated output of 110 kW at 3,800 rpm. As a result of its regulated two-stage turbocharging, the engine offers the driver not only a more spontaneous response, particularly when pulling away, accelerating and on hills, but also a higher and more pronounced torque characteristic.
Regulated two-stage turbocharging consists of two differently sized turbochargers arranged in series: a large low-pressure turbocharger and a small high-pressure turbocharger. In this arrangement, the turbochargers are tuned in such a way that both of them are active at all engine operating points. At low engine speeds, the smaller high-pressure turbocharger guarantees a much-improved response with no turbo lag. As the engine speed rises, the larger low-pressure turbocharger becomes more and more effective until it completely takes over from its smaller high-pressure partner. The boost pressure is regulated by a bypass in the high-pressure turbocharger. This prevents drops in boost pressure, such as those that occur, for example, in sequential turbocharging systems.
A further development of regulated two-stage turbocharging is the self-regulating compressor bypass. This is being used for the first time in the Mercedes-Benz Sprinter. It takes over the job of the vacuum-controlled compressor bypass valve, which has the function of bypassing the high-pressure turbocharger at high engine loads. Eliminating the need for external control not only cuts production costs but also allows a greater amount of flexibility in arranging the components.