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1. A low pressure EGR apparatus applied to an internal combustion engine having a supercharger installed in an intake and exhaust system, wherein the low pressure EGR apparatus recirculates a portion of exhaust gas, which has passed through an exhaust gas purifying device provided in an exhaust passage of the internal combustion engine, to an intake passage at a location that is on an upstream side of a compressor of the supercharger, as low pressure EGR gas, the low pressure-EGR apparatus comprising:
a low pressure EGR passage that connects between a portion of the exhaust passage, which is located on a downstream side of the exhaust gas purifying device, and a portion of the intake passage, which is located on an upstream side of the compressor; a low pressure EGR valve that adjusts a flow quantity of the low pressure EGR gas to be recirculated into the intake passage through the low pressure EGR passage; a valve drive device that drives the low pressure EGR valve; a throttle valve that is installed in one of the exhaust passage and the intake passage, wherein the throttle valve reduces an opening degree of the one of the exhaust passage and the intake passage to increase the flow quantity of the low pressure EGR gas to be recirculated into the intake passage; a synchronizing mechanism that drives the throttle valve in a closing direction for closing the one of the exhaust passage and the intake passage synchronously with a valve opening movement of the low pressure EGR valve, which is a rotational movement of the low pressure EGR valve in an opening direction for opening the low pressure EGR passage, wherein the synchronizing mechanism drives the throttle valve in an opening direction for opening the one of the exhaust passage and the intake passage synchronously with a valve closing movement of the low pressure EGR valve, which is a rotational movement of the low pressure EGR valve in a closing direction for closing the low pressure EGR passage, wherein the synchronizing mechanism includes a drive plate that is rotated integrally with the low pressure EGR valve, a driven plate that is rotated integrally with the throttle valve, and a cam mechanism that transmits rotation of the drive plate to the driven plate; a failure mode setting mechanism that sets a failure mode by limiting rotation of the throttle valve and rotation of the low pressure EGR valve and sets the failure mode in a state where coupling between the drive plate and the driven plate is released due to malfunction of the cam mechanism; and a failure mode determining device that determines whether the failure mode is set based on a rotational position of the low pressure EGR valve, wherein: the failure mode setting mechanism includes:
a spring that urges the throttle valve in an opposite direction, which is opposite from the closing direction of the throttle valve for closing the one of the exhaust passage and the intake passage synchronously with the valve opening movement of the low pressure EGR valve;a throttle valve side stopper that mechanically stops the throttle valve at a predetermined rotational position when the throttle valve is urged by the spring and is thereby rotated; anda valve side stopper that mechanically stops rotation of the low pressure EGR valve in response to a stop position of the throttle valve; the failure mode determining device includes a valve angle sensor that senses a rotational position of the low pressure EGR valve as a valve angle; and the failure mode determining device determines that the failure mode is set in a case where the valve angle, which is sensed with the valve angle sensor, is the rotational position of the low pressure EGR valve, which is stopped by the valve side stopper, at a time of rotating the low pressure EGR valve from a full close position of the low pressure EGR valve, at which an opening degree of the low pressure EGR valve is minimum, to a full open position of the low pressure EGR valve, at which the opening degree of the low pressure EGR valve is maximum, wherein: the throttle valve side stopper is placed to oppose the driven plate in a rotational direction of the driven plate for rotating the driven plate integrally with the throttle valve through urging of the throttle valve with the spring; and the throttle valve stops at the predetermined rotational position when the driven plate contacts the throttle valve side stopper. |
