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(11) | EP 0 778 409 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Abnormality detecting apparatus for exhaust gas recirculation system for use in engine |
| (57) Disclosed is an abnormality detecting apparatus for an exhaust gas recirculation
(EGR) system for an engine. The EGR system (16) has a pressure responsive valve (EGR
valve: 18) which is actuated in response to the negative pressure and atmospheric
pressure for controlling EGR, and a pressure regulating valve (EVR valve: 19) which
selectively supplies the negative pressure or the atmospheric pressure to the EGR
valve (18) for its actuation. The EVR valve (19) has a port (19a) communicating with
the EGR valve (18), a port (19b) for supplying the negative pressure and a port (19c)
for supplying the atmospheric pressure. A filter (22) provided at the atmospheric
air port (19c) serves to prevent dust or mud from entering the EVR valve (19). When
the EGR valve (18) is to be open, the EVR valve (19) is actuated to supply the negative
pressure to the EGR valve (18). When the EGR valve (18) is to be closed, the EVR valve
(19) is actuated to supply the atmospheric pressure to the EGR valve (18). An electronic
control unit (ECU: 41) measures the required time at the time of closing the EGR valve
(18) from the open state. When determining that the required time is greater than
a reference value, the ECU (41) detects an abnormality in the EGR system (16) which
has occurred due to the excessively large permeability resistance of the filter (22). |