Importance

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Abstract

An apparatus and method for vehicle emissions control are disclosed. More particularly, an apparatus and method for insuring that the temperature of a vehicle's exhaust gas stream entering the underfloor catalytic converter during engine operation does not exceed the temperature at which the capability of the multi-functional catalyst in the converter to absorb NO.sub.x starts to fall off. A first temperature sensor is provided in the exhaust outlet leading from the exhaust manifold of the engine and a second temperature sensor is provided in the catalytic converter. The catalytic converter contains a multi-functional catalyst such as a three-way conversion catalyst and a NO.sub.x trap as well as a NO.sub.x sensor at its outlet for sensing when NO.sub.x breakthrough is occurring. The sensors transmit their readings to a controller which transmits signal to a proportional valve located in the exhaust outlet downstream of the first temperature sensor. In response to the signals received from the controller, the proportional valve divides the exhaust gas stream received from the engine exhaust manifold into a first stream in communication with the catalytic converter and a second stream in communication with a heat exchanger. Any stream exiting the heat exchanger is then blended with the non-heat exchanged stream and the blended stream is passed into the catalytic converter. The amount of the exhaust gas stream in the first conduit will vary from that in the second conduit such that the temperature entering the catalytic converter is maintained in the range of about 300 to about 600.degree. C. during the lean mode operation of the engine and further such that the multi-functional catalyst is periodically purged of NO.sub.x and/or SO.sub.x.

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First Claim