Page 239 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Other Methods 22 1

VolkswagenAG

In the method of DE4331 153 (1994) the significant variations of the amplitudes and/or the
airhe1 ratio oscillation frequencies and/or the oscillation positions (phase shift) of the
upstream and downstream lambda sensors consist the criteria of evaluation of a degraded
catalytic converter. The evaluation takes place at partial load of the engine.

Roth-Tecltnik GmbH & Co. Forschung flr Automobil- und
Umwelttechniek

In the method of WO9516109 (1995) the partial oxygen pressure is measured upstream and
downstream of the catalytic converter by means of two lambda probes. The difference of the
measured oxygen partial pressures gives an indication of the condition of the catalytic
converter.

Unisia Jecs Corp.

In JP7109918 (1995) the diagnosis of the efficiency of the catalytic converter is based on the
deviation of the output value of the downstream oxygen sensor from a reference value for a
desired aidfuel ratio in the feedback control.

In JP7189780 (1995) the diagnosis of the efficiency of the catalytic converter is based on the
comparison of the oscillation frequencies of the output signals of the upstream and the
downstream sensor. The method also detects a possible defect of the downstream oxygen
sensor.

in the method of US5533332 (1996), the engine airhe1 ratio is feedback controlled by means
of the output of the downstream oxygen sensor only, so that the air/fuel ratio approaches a
target value. During the feedback control, the phase difference between the output signals of
the upstream and downstream oxygen sensors is detected, and the performance of the catalytic
converter is judged by means of this phase difference.

In JP8284649 (1996) a predetermined diagnostic region is detected, in which the degradation
assessment is performed. During feedback control of the engine air/hel ratio, the ratio of
reversals of the output signals of the upstream and downstream sensor is formed for a number