| Following its successful debut in the BMW 535d, regulated 2-stage turbocharging from BorgWarner Turbo Systems is now also serving the commercial vehicle market. In close co-operation with MAN Nutzfahrzeuge, the turbocharger specialist has developed a regulated 2-stage turbocharger system called R2S that allows an infinitely variable adaptation of the turbine and compressor side to any engine operating point. This pioneering technology is now being used in the new MAN TGL for the 151 kW (206 bhp) four-cylinder D0834 LFL 42 from the D08 common-rail engine series. Series production started in spring this year.
Borg Warner's RS2 2-stage turbocharger that is being used in the new MAN TGL |
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Regulated 2-stage turbocharging from BorgWarner Turbo Systems is designed to meet the increasing demands for more power output and emissions. At low revolutions, the smaller high-pressure turbocharger ensures a much more spontaneous engine response with no turbo lag. As the engine speed rises, the high-pressure turbocharger is supported by the larger low-pressure turbocharger, initially as a pre-compressor, providing a constant increase in power. As a result of this regulated 2-stage turbocharging, the 4.6 litre 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. Maximum torque is 830 Nm at 1,400 rpm. This puts the four-cylinder engine clearly ahead of its competitors. In spite of the increased power output, the engine is nevertheless extremely economical and has very low emissions.
The introduction of regulated 2-stage turbocharging now provides commercial vehicle diesel engines with a technology that can meet the increasing power requirements and comply with future emissions standards. In the months to come, it is anticipated that additional commercial vehicle engines will benefit from this innovative turbocharger technology from BorgWarner Turbo Systems.
Turbocharging in Two Stages: The Principle of Regulated 2-Stage Turbocharging
The R2S regulated 2-stage turbocharging consists of two differently sized turbochargers arranged in series: a large low-pressure turbocharger and a small high-pressure turbocharger. In contrast to passenger car applications, regulated 2-stage turbocharging for commercial vehicles has only one bypass valve as an actuator on the 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, in other words at low exhaust flow rates, the low-pressure turbocharger performs only a small part of the turbocharging. The bypass on the high-pressure turbine is completely closed. As a result, the energy from the exhaust gas is used entirely to compress the fresh air in the high-pressure compressor. In the medium and high engine speed range, part of the exhaust gas is diverted through the bypass on the turbine side. During this process, the exhaust energy is not wasted but is now fully available to the low-pressure turbine. The boost pressure is regulated by the external bypass. This allows continuous control without any drop in boost pressure, as occurs, for example, in register turbochargers. As the engine speed rises, more and more of the exhaust energy bypasses the high-pressure stage and is fed directly to the low-pressure stage. As an alternative to a turbocharger with a turbine bypass valve, a turbocharger with variable turbine geometry (VTG) can be used in the high-pressure stage to control the boost pressure. The VTG can also by adjusted by a pneumatic or electronic actuator.
Regulated 2-stage turbocharging therefore allows infinitely variable adjustment of the turbine and compressor side in accordance with the operating conditions.
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