Page 193 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Chapter I. 10

NGK Spark Plug Co.

In the method of US4884066 (1989) the airhel ratio oscillates around the stoichiometric
value from lean to rich and vice versa. If the amplitude of the oscillation of the output signal of
the downstream sensor is bigger than a predetermined value the catalytic converter is
considered as deteriorated. The sensor used downstream of the catalytic converter is
constructed so that its output and the aidfirel ratio are in direct proportional relationship.

In the method of US5157921 (1992) the engine airhe1 ratio forcibly oscillates and a ratio of
the amplitudes of the oscillating output signals of the upstream and downstream sensors is
formed. The ratio can have one of the following forms:

-hl
f?, = - 100
x
a.
where
al, bl: output amplitudes of upstream and downstream sensors respectively (fig. 80), or

175