This invention relates to a vehicle-mounted internal combustion engine provided with an EGR (exhaust gas re-circulation) system.
In the internal combustion engines such as gasoline engines and Diesel engines, EGR recirculating the exhaust gas is carried out in order to reduce NOx in the exhaust gas. For this EGR, an EGR line having an EGR valve at a mid-point for controlling an EGR amount is arranged branching from the exhaust line and joining to the intake line. Moreover, an EGR controller for controlling this EGR valve is also arranged.
An internal combustion engine performing this EGR has a problem of sulfuric acid corrosion caused by the EGR gas confined in the EGR line when the operation of the internal combustion engine is stopped.
Namely, when the operation of the internal combustion engine is stopped, since high temperature EGR gas containing moisture are confined in the EGR line, the contained moisture is condensed when the internal combustion engine is cooled and the EGR gas is cooled. Then, the condensed water adheres to the EGR line, the EGR valve, etc. Since the condensed water reacts with sulfur content in the exhaust gas to form sulfuric acid, the EGR piping, the EGR valve, etc. are corroded with this sulfuric acid.
In order to cope with this, an EGR valve anticorrosion system described in the conventional Patent Publication 2737412 (page 2), although this is suitable for an internal combustion engine using an alcohol fuel, forcibly makes the EGR valve open by interlocking it with the ignition key of the engine when the engine comes to a halt state from an operational state.
However, in order to correspond to the reinforcement of emission gas control in recent years, the EGR amount is increased for promoting an effect of NOx reduction, and condensed water formed in the EGR line is also increased in the amount associated therewith. Therefore, there is a problem that the corrosion cannot fully be coped with by controlling the EGR valve to be open only when the ignition key is turned off.
Moreover, thanks to the widespread use of idling stop systems, it has become necessary to prevent the condensed water from being formed by scavenging the EGR line also before or after the idling stop. However, since this idling stop is not always interlocked with the ignition key, there is another problem that the corrosion problem cannot fully be coped with by open-control of the EGR valve only at the time of key-off.