An exhaust gas recirculation (EGR) passage is connected with an intake passage (a bypass passage bypassing a supercharger) of an engine. The EGR passage includes, in a position close to a connection port to the intake passage, an expanding portion in which a passage cross-sectional area expands and which lowers a flow speed of EGR gas so as to reduce an uneven flow, in the connection port, of the EGR gas flowing into the intake passage.

An exhaust gas recirculation (EGR) passage is connected with an intake passage (a bypass passage bypassing a supercharger) of an engine. The EGR passage includes, in a position close to a connection port to the intake passage, an expanding portion in which a passage cross-sectional area expands and which lowers a flow speed of EGR gas so as to reduce an uneven flow, in the connection port, of the EGR gas flowing into the intake passage.

An EGR device is provided with: an EGR passage for allowing a portion of exhaust gas from an engine to flow to an intake passage; an EGR valve for adjusting an EGR flow rate through the EGR passage; a throttle valve provided in the intake passage; and an electronic control device which calculates a fully closed reference intake pressure based on an operating state of the engine during EGR valve fully-closing, and which diagnoses an abnormality due to valve-opening locking of the EGR valve based on the calculated fully closed reference intake pressure. The ECU determines a foreign matter biting abnormality of the EGR valve based on the intake pressure, and based on the result of adding the fully closed reference intake pressure, calculated according to the rotational speed and the load of the engine, to an intake-pressure increase allowance calculated according to the rotational speed.

A hot gas exhaust recirculation valve includes a housing containing a duct for conducting gases, a drive chamber, and a valve stem which is mounted in the housing. The valve stem can be displaced in its longitudinal direction thereof and extends from the drive chamber into the duct. The end of the valve stem that is situated in the drive chamber is coupleable to a drive device. A closing body is fastened to the other end of the valve stem. The closing body is situated in the duct and has a closed position in which it separates an upstream section of the duct from a downstream section of the duct. A sealing ring surrounds the valve stem and is arranged between the duct and the drive chamber. The valve stem is supported within two bearing bushings that are spaced apart from each other, between which the sealing ring is arranged.

A hot gas exhaust recirculation valve includes a housing containing a duct for conducting gases, a drive chamber, and a valve stem which is mounted in the housing. The valve stem can be displaced in its longitudinal direction thereof and extends from the drive chamber into the duct. The end of the valve stem that is situated in the drive chamber is coupleable to a drive device. A closing body is fastened to the other end of the valve stem. The closing body is situated in the duct and has a closed position in which it separates an upstream section of the duct from a downstream section of the duct. A sealing ring surrounds the valve stem and is arranged between the duct and the drive chamber. The valve stem is supported within two bearing bushings that are spaced apart from each other, between which the sealing ring is arranged.

An exhaust gas recirculation (EGR) passage is connected with an intake passage (a bypass passage bypassing a supercharger) of an engine. The EGR passage includes, in a position close to a connection port to the intake passage, an expanding portion in which a passage cross-sectional area expands and which lowers a flow speed of EGR gas so as to reduce an uneven flow, in the connection port, of the EGR gas flowing into the intake passage.

This engine system is provided with a throttle device, an EGR valve, and an ECU. The ECU diagnoses an abnormality of the EGR valve on the basis of an operating state during an engine deceleration, and diagnoses combustion deterioration of an engine on the basis of a crank angle speed change during the engine deceleration (not during a fuel cut-off). The ECU executes an engine stall avoidance control with the throttle device when it is determined there is an abnormality in the EGR valve, makes a final determination that the EGR valve has an abnormality and continues the engine stall avoidance control when it is determined thereafter that there is combustion deterioration, and makes a final determination that the EGR valve is normal and cancels the engine stall avoidance control when it is determined that there is no combustion deterioration.

This engine system is provided with a throttle device, an EGR valve, and an ECU. The ECU diagnoses an abnormality of the EGR valve on the basis of an operating state during an engine deceleration, and diagnoses combustion deterioration of an engine on the basis of a crank angle speed change during the engine deceleration (not during a fuel cut-off). The ECU executes an engine stall avoidance control with the throttle device when it is determined there is an abnormality in the EGR valve, makes a final determination that the EGR valve has an abnormality and continues the engine stall avoidance control when it is determined thereafter that there is combustion deterioration, and makes a final determination that the EGR valve is normal and cancels the engine stall avoidance control when it is determined that there is no combustion deterioration.

A system for deactivating at least one predetermined cylinder of an operational multicylinder engine, with each cylinder including an intake duct with an inlet connected to the intake manifold and an outlet connected to the cylinder in order to allow the intake of combustion gases from the intake manifold to the cylinder, may include a first movable sealing means suitable for sealing the inlet of said intake duct of the predetermined cylinder, a recirculation duct suitable for connecting said intake duct of said predetermined cylinder to an exhaust gas supply, and a second movable sealing means suitable for sealing said recirculation duct.

A system for deactivating at least one predetermined cylinder of an operational multicylinder engine, with each cylinder including an intake duct with an inlet connected to the intake manifold and an outlet connected to the cylinder in order to allow the intake of combustion gases from the intake manifold to the cylinder, may include a first movable sealing means suitable for sealing the inlet of said intake duct of the predetermined cylinder, a recirculation duct suitable for connecting said intake duct of said predetermined cylinder to an exhaust gas supply, and a second movable sealing means suitable for sealing said recirculation duct.