EGR Recirculation at Low Load in Internal Combustion Engines

This invention relates to induction systems for internal combustion engines, and especially to an improved way of achieving exhaust gas recirculation therein.

It has been recognized that exhaust gas recirculation, which consists of bringing back a part of the exhaust gas to the intake side of an internal combustion engine is effective in limiting the generation of nitrogen oxides in the combustion chamber. However, too high a concentration of recirculated exhaust gas causes deterioration in the driveability of the vehicle. Therefore, in conventional internal combustion engines provided with exhaust recirculation systems, the recirculation rate is usually limited, which as a practical matter limits the effect in diminishing the amount of nitrogen oxides produced in the combustion chamber.

It is an object of this invention to overcome the above-described shortcoming of the prior art, by providing an improved internal combustion engine which can accommodate a larger rate of exhaust gas recirculation without being accompanied by deterioration of the driveability of the vehicle.

This invention is carried out with an internal combustion engine which has a principal induction passage leading to an intake port of the engine in which is positioned a principal throttle valve. An auxiliary throttle valve is provided in the principal induction passage, and an auxiliary induction passage extends from a point between the two throttles to a region adjacent to the intake port of the combustion chamber. The auxiliary induction passage has a smaller cross-sectional area than that of the principal induction passage. An exhaust gas recirculation system is provided which includes a conduit extending from the exhaust pipe to the principal induction passage. The exhaust gas is delivered to a portion of the induction passage where pulsations will be absorbed. The auxiliary throttle valve is closed at light and medium loads. Accordingly, the recirculating exhaust gas is fed to the combustion chamber through the auxiliary induction passage at least during the light and medium load operation of the engine. Thus, in the light and medium load operation of the engine, the recirculated exhaust gas is jetted into the combustion chamber at a high velocity to form a strong swirl in the combustion chamber so that the exhaust gas and the mixture in the combustion chamber are mixed uniformly. Therefore it becomes possible to increase the amount of recirculated exhaust gas (i.e., to increase the recirculation rate) while still maintaining stable combustion in the combustion chambers. Accordingly, the amount of nitrogen oxides produced can be significantly reduced without deteriorating the driveability of the vehicle.

According to a preferred but optional feature of the invention, the exhaust gas is returned to the principal induction passage between the throttles in a place where the passage volume is enlarged so that it serves as a surge tank or plenum to absorb or cushion the surging or pulsation of exhaust pressure, thereby insuring a more uniform mixing of the recirculated exhaust gas and the combustable mixture.

FIG. 1 is a fragmentary side elevation of an internal combustion engine incorporating a system according to the invention with certain portions being shown schematically; and

FIG. 2 is a view similar to FIG. 1 showing another embodiment of the invention.

With reference to FIG. 1, which shows the presently preferred embodiment of the invention, an internal combustion engine is shown with a plurality of cylinders 2 (only one of which appears in the drawing) formed in a cylinder block 1. A piston 3 is adapted to be reciprocally moved in each of cylinders 2. A cylinder head 4 is secured to the upper end of each cylinder block 1 and cooperates with the cylinder 2 and piston 3 in defining a combustion chamber 9. An intake port 5 and an exhaust port 6 are formed in the cylinder head 4 and open into the combustion chamber 9.

The intake exhaust ports 5 and 6 are provided with respective inserted valve seats 7 and 8 around their peripheries, while cooperative intake and exhaust valves 10, 11, respectively, are mounted on the cylinder head 4. The valves 10 and 11 are operated to open and close their respective ports 5 and 6 in synchronization with movement of the piston 3 by a valve actuating mechanism of any known type.

The cylinder head 4 has an ignition plug 12 positioned therein within each combustion chamber 9. The exhaust ports 6 of each respective combustion chamber 9 is connected to an exhaust manifold 13 in a known manner, while the intake port 5 is connected to a principal induction passage 15 formed by an intake manifold to which air/fuel mixture is supplied by carburetor 16 which has principal throttle valve 16a (the primary throttle valve) and a secondary throttle valve 16b.

The exhaust gas recirculation system comprises a recirculation passage 17 which opens at one end in the exhaust manifold 13 and at its other end in induction passage 15 downstream from principal throttle valve 16a. A control valve 18 is disposed in the exhaust gas recirculation passage 17. The control valve is adapted to be actuated by a pressure difference generated in part by a vacuum line 22 which in turn is adapted to be opened and closed by an electromagnet valve 21 combined with a switch 20 all in a known manner. The switch 20 is associated with an accelerator pedal 19 so that the control valve 18 will open the recirculation passage when the engine is operated at light and medium load ranges.

An auxiliary throttle valve 23 is placed in the principal induction passage 15 downstream from the throttle valves 16a and 16b. Auxiliary throttle valve 23 is adapted to be actuated by, for example, a vacuum actuator 24 which is adapted to be operated in response to the intake vacuum established in the principal induction passage 15 between throttle valves 16a and 16b and the auxiliary throttle valve 23, so it closes the principal induction passage 15 in the light and medium load range.

An auxiliary induction passage 25 is provided to detour or by-pass auxiliary throttle valve 23. Auxiliary induction passage 25 has its upstream side opening in the principal induction passage 15 at a location between the two throttles i.e., upstream from auxiliary throttle 23 and downstream from the principal throttle valve 16a. Its downstream discharge port 26 comprises a nozzle located in the vicinity of intake port 5 which is directed toward the combustion chamber 9. It will be noted that the discharge port 26 and associated nozzle are disposed at a substantially different angle from the portion of the main intake passage at the port 5. Therefore, a charge issuing from the auxiliary induction passage 25 will enter the chamber 9 at a substantially different angle from the charge entering from the port 5.

The auxiliary induction passage 25 has a much smaller cross-section area than that of the principal induction passage 15. Therefore, when the auxiliary throttle valve 23 is closed, the air/fuel mixture flows through the auxiliary induction passage 25 instead, and into the combustion chamber 9 at an extremely high speed through the nozzle 26.

FIG. 2 shows the engine of FIG. 1 utilizing fuel injection techniques instead of a carburetor. Like numbers are used for like parts, and the description of these components will not be repeated. Auxiliary passage 25 in FIG. 2 extends alongside passage 15. In this embodiment air and recirculated exhaust gas flow in passages 15 and 25, and the fuel is injected toward intake port 5 by fuel nozzle 30. At the upstream end there is an air metering means (not shown) such as a primary throttle valve for supplying air to the induction passages, and a means (not shown) for metering fuel is also provided. Operation of this system is the same as described before, except that only air flows in passages 15 and 25, instead of air/fuel mixture.

It will be noted that the exhaust gas returned to the induction system through the control chamber 18 will enter into the induction system at an enlarged volume of the intake manifold system at the point where the auxiliary induction passage 25 has its inlet. This enlarged volume acts like a plenum chamber so as to damp pulsations in the exhaust gas from the individual chambers 9. Thus, pulsations are not experienced at the point of discharge into the combustion chambers 9.

As has been described, in the illustrated internal comnbustion engine the auxiliary throttle valve is closed at light and medium load ranges at which exhaust gas recirculation takes place, so that the combustible air/fuel mixture including the recirculated combustion gas is jetted into the combustion chamber at a high speed so as to create a strong swirl of the combustion chamber, thereby to insure a good mixing of the air/fuel mixture with a recirculated combustion gas and consequent good ignitability.

Further with regard to FIG. 1 it will be seen that the exhaust gas conduit 17 enters the principal induction passage in the left-hand barrel of the carburetor where a wall stands between it and the entrance to the auxiliary induction passage 25. Therefore, there is no direct confrontation of the two conduits and no direct transmission to the auxiliary induction passage of pulsations in the exhaust gases.

This invention is not to be limited by the embodiments shown in the drawings and described in the description, which are given by way of example and not of limitation, but only in accordance with the scope of the appended claims.