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Control valve is key to twin turbo
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01/03/2007
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The parallel sequential dual-stage turbocharger developed by Honeywell for the new Peugeot 407, 607 and Citroën C5 and C6 diesel engines has at its heart a patented progressive control valve, writes Roger Bishop.
These first applications followed three years of development work.
In the design two small turbos work side by side. One operates at low engine revolutions as the second idles. At high engine speeds both units work in tandem. This arrangement is in contrast to the more traditional serial sequential dual-stage configuration, in which a smaller high-pressure turbo works in advance of a much larger turbo.
The control valve uses pressurised air from the first turbo both to aspirate the second turbo when it is idling – avoiding any possibility of oil leakage – and to accelerate it when additional boost is required by the engine. The system also includes a position feedback sensor controlled by the ECU.
The design chosen was a sliding-piston valve – against throttle or swing valve concepts – for its optimal sealing and controllability characteristics. It was based on Honeywell’s experience with VNT-OP turbo technology. The piston is pressure balanced to minimise actuator force, eliminate any possibility of sticking and to allow it to be small and compact.
The unit is said to boost torque by 30% compared with the naturally aspirated 2.2 litre diesel and improves third-gear acceleration in the 30 to 60km/h range by as much as 50%. The turbocharged 2.2 litre HDi unit delivers 330Nm of torque at 1,300rpm and 370Nm at 1,500rpm.
Honeywell also is supporting the development of several serial sequential dual-stage turbochargers. The first is expected to be seen during 2007.
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Author
Roger Bishop
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