| 摘要 |
<p>PURPOSE: To detect the trouble of the conversion efficiency of a catalyst by testing the amplitude of air/fuel fluctuations at a time when a hot exhaust gas oxygen(HEGO) sensor behind a catalyst is used in air/fuel feedback of a low gain. CONSTITUTION: A ternary catalyst 30 has a downstream side exhaust gas oxygen(EGO) sensor 31 for supplying a signal output to a low-pass filter 33. The low- pass filter 32 removes the high frequency combustion noise generated from an engine. The signal from the lowpass filter 32 passes through an amplitude detection mechanism 3, a speed torque gate 34, a sample hold circuit 35 and a running average circuit 36 to advance to an obstacle display circuit 37. A block 38 adds speed and torque signals to a speed torque gate 34 and the sample hold circuit. The deterioration of catalyst conversion efficiency is detected by calculating HEGO sensor output fluctuations compared with the value measured by a good catalyst. Especially, when the amplitude of HEGO sensor output voltage fluctuations becomes lower than a preset value (e.g; the value of an amplitude detection circuit), the catalyst is judged to be out of order to energize the obstacle display circuit 37.</p> |
