Anti-lag system

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An anti-lag system , or ALS for short, or bang-bang system is the term used in racing to describe an automatic air circulation system that is noticeable due to its misfire (popping noises). The ALS is intended to prevent the turbocharger from decelerating in order to avoid turbo lag (delayed power delivery ).

Mode of action

The effect is based on the following measures:

  • Part of the pent-up air is diverted between the compressor wheel (compression of the intake air) of the turbocharger and the closing / closed throttle valve (see also air circulation valve )
  • The other part of the air is fed into the cylinder, mixed with fuel and enriched in the process
  • The diverted air is fed back in front of the turbine wheel (normally driven by the exhaust gas) of the turbocharger
  • The ignition point is moved to approx. 20 ° after TDC (retarded ignition)

The rich and late-ignited mixture in the cylinder is partially unburned when it leaves the cylinder through the exhaust valve. The diverted fresh air is mixed in upstream of the turbine wheel so that the dragged-out combustion is continued upstream of the turbine wheel. Some of the combustion still takes place in the tailpipe, so that flames can hit the tailpipe.

This keeps the turbocharger at high speed even though the gas has been removed. The measure is considered to be particularly effective if the competition regulations prescribe an air flow limiter (restrictor). The restrictor delays the rev up of a braked turbocharger, this is to prevent the ALS.

The disadvantages are considered

  • higher fuel consumption
  • Reduction in the service life of the exhaust system (less relevant for racing vehicles)

literature

  • Gert Hack, Iris Langkabel: Turbo and compressor motors . 1st edition. Motorbuch Verlag, Stuttgart 1999, ISBN 3-613-01950-7 .
  • Ford: Focus ST with anti-lag function . In: ATZ Extra . Springer Fachmedien GmbH, August 1, 2019, ISSN  2195-1454 , p. 13 .

Individual evidence

  1. ↑ Michael Trzesniowski: drive . Springer Fachmedien GmbH, Wiesbaden 2017, ISBN 978-3-658-15534-6 , A.4 4 assembly modules, p. 112 .