| 摘要 |
PROBLEM TO BE SOLVED: To provide a degradation diagnostic device of a linear air-fuel ratio sensor which can analyze degradation status in detail. SOLUTION: A liner air-fuel ratio sensor feeds back to a feedback control system the output PF in proportion to an oxygen concentration in exhaust gas so that feedback control is executed. When a prescribed diagnostic condition is established, an impulse-like disturbance is output to the feedback control system. After the output of the disturbance, a differential value D<SB>O2</SB>of the output PF of the liner air-fuel ratio sensor SW4 is computed. At least one of waste time and time constant is computed as a determining parameter for degradation determination. The establishment of the diagnostic condition leads to reduction in gain of the main control element. As a result, the detailed analysis of the degradation status can be materialized. Although the disturbance is outputted, the divergence of the feedback control system can be prevented, which allows the stability to be maintained. COPYRIGHT: (C)2007,JPO&INPIT
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