Oxygen Sensor System

During recent years the laws which regulate exhaust gas emissions have become increasingly strict. The constant volume sampling or CVS test is used deformine allowable limits of hydrocarbons, carbon-monoxide and oxides of nitrogen. It is possible to meet the present emission limits with secondary air injection, catalytic converter and E.G.R. (exhaust gas recirculation).

This emission control system has a number of disadvantages:

o The E.G.R. system increases fuel consumption considerably and decreases overall driveability and performance.

o The power required to drive the air pump lowers performance and increases fuel consumption, o The additional emission components which are required result in increased manufacturing costs. The additional number of parts increases the probability of something failing.

The oxygen sensor emission control system has been chosen for the Porsche 924 turbo in order to comply with the emission regulations for 1980.

The oxygen sensor system consist of:

An oxygen sensor (C) which measures the oxygen in the exhaust; an electronic control unit (A); and a frequency valve (F) operated by the control unit which adjusts the air/fuel mixture.

A pair of micro-switches change the control unit signal at idle (D) and provide full load enrichment at full throttle (E). A relay (B) also provides full load enrichment when the engine speed exceeds 3.500 ± 150 R.P.M.

A new 3-way catalytic converter is used which replaces the standard catalytic converter, air-pump and E.G.R. system.

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