Clean air systems

Automotive Design & Production, June, 2005

Mann Hummel's secondary air charger replaces a conventional belt-driven or electric secondary air pump with a unit that is both smaller and lighter. It features a turbocharger-like turbine and compressor wheel on a common shaft that is driven by the difference in air pressure at the throttle body. The compressor wheel introduces fresh air into the exhaust system to improve the oxidation of both hydrocarbon (HC) and carbon monoxide (CO) emissions, and reduces the light-off time of the catalyst. Plastic is used for the turbine and compressor wheels, which have low inertia and mass. This makes the unit more responsive and lighter than conventional designs.

In 2007, California and some Northeastern states will severely limit HC emissions once the engine is turned off. The so-called "hot stop" hydrocarbon emissions must not exceed 0.054 g--the equivalent of one drop of fuel--in a well-defined 24-hour test cycle. Since they escape up the intake manifold and into the air filter from the intake and exhaust valve that remain partially open, Mann Hummel created an absorptive hydrocarbon trap that is permanently installed in the vehicle intake system and has a service life of 15 years or 150,000 miles. The HC molecules are released back into the intake air stream when the engine is restarted.

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