This invention relates to an internal combustion engine with an exhaust gas recirculation system.
Well known are exhaust gas recirculation engines which recirculate a part of the exhaust gas extracted from an exhaust system of the engine into an intake system of the engine for reducing harmful contaminants, especially nitrogen oxides (NO.sub.x) contained in the exhaust gas.
One of the well known engines which has been developed is an internal combustion engine with an exhaust gas recirculation system comprising valve device for controlling the exhaust gas recirculation. The exhaust gas recirculation control valve device communicates an exhaust passage of the engine with an intake passage of the engine and is provided with a diaphragm chamber, partitioned by a diaphragm, and a constant pressure chamber, partitioned by a valve body which is actuated by the diaphragm. The engine further comprises a modulator valve device for modulating a vacuum signal which is transmitted from a first port disposed at a position upstream of a throttle valve of a carburetor to the diaphragm chamber. The modulator valve device is provided with an upper diaphragm chamber, which is communicated with a second port disposed at a position nearer to a venturi portion of the carburetor than the first port and communicated with a vacuum control valve device for controlling the vacuum pressure in accordance with changes in intake vacuum pressure, and a lower diaphragm chamber communicating with the constant pressure chamber of the exhaust gas recirculation control valve device.
In the above-described internal combustion engine with an exhaust gas recirculation system, while the engine load is low, since the intake vacuum of the engine becomes high, the vacuum control valve is actuated and the exhaust gas recirculation control valve device is closed. Therefore, the exhaust gas is not recirculated. When the load of the engine reaches a predetermined level, the intake vacuum becomes low. On the other hand, the constant pressure chamber of the exhaust gas recirculation control valve device is controlled so as to maintain a predetermined pressure which is almost equal to the atmospheric pressure. As a result, a part of the exhaust gas, the amount of which is proportional to that of the intake gas mixture, is recirculated into the engine. When the load of the engine is maximum, the pressure at the second port becomes vacuum pressure, and then, the pressure in the upper diaphragm chamber of the modulator valve device becomes vacuum pressure. In other words, since the pressure in the upper diaphragm chamber, becomes vacuum pressure, the exhaust gas recirculation control valve device is closed because the vacuum pressure in the constant pressure chamber is controlled so that it equals the pressure in the upper diaphragm chamber. As a result of the vacuum in the constant pressure chamber, the recirculation of the exhaust gas from the exhaust passage to the intake passage is stopped. As mentioned above, a desired amount of exhaust gas is recirculated in accordance with changes in the engine loads.
The above-mentioned internal combustion engine with an exhaust gas recirculation system may cause a defect that, when a vehicle in which the engine is installed is started or accelerated, the torque of the engine will be decreased and the speed of the vehicle will be temporarily lowered. This phenomenon is called "breathing phenomenon". When the breathing phenomenon continues for a certain period of time, a phenomenon which is called "surging phenomenon" is caused and the driveability of the vehicle is reduced. When such breathing and surging phenomena are caused, the driver may step on the accelerator gas pedal excessively, which can result in a defect that the amount of carbon monoxide (CO) emitted from the engine is increased.