Exhaust gas recirculation control device for internal combustion

Abstract

A flow control device for use in an exhaust gas recirculation system of an internal combustion engine and adapted to control the amount of engine exhaust gases recirculated to an intake manifold of the engine in a manner optimum for reducing toxic nitrogen oxides contained in the engine exhaust gases without impairing engine operation. The flow control device is comprised of an exhaust gas recirculation passage, a flow control valve located in the exhaust gas recirculation passage and responsive to the position of a carburetor throttle valve of the engine, and a flow restricting means located in the exhaust gas recirculation passage in series with the flow control valve. The flow restricting means includes another flow control valve responsive to a signla indicative of cold or light load operating conditions of the engine.

Description

This invention relates in general to an exhaust gas recirculation system for internal combustion engines and, more particularly, to a flow control device for use in the exhaust gas recirculation system adapted for controlling the flow of exhaust gases recirculated to an intake manifold of the engine.

In conventional exhaust gas recirculation systems, it has been common practice to recirculate a portion of engine exhaust gases in a continuous fashion to an intake manifold of the engine with a view to reducing the quantity of toxic nitrogen oxides contained in the engine exhaust gases. A difficulty is encountered in this prior practice is that continuous recirculation of the engine exhaust gases without respect of the engine operating conditions results in unstable engine operation, decreased power output and contamination within the engine cylinders. To overcome this drawback, it has heretofore been proposed to have an exhaust gas recirculation passage provided with a flow control valve which is mechanically linked with a carburetor throttle valve of the engine. This flow control valve is so arranged as to be actuated in response to opening and closing movements of the carburetor throttle valve for thereby varying the sectional area of the passage through which the engine exhaust gases flow. With this arrangement, it is quite difficult to control the flow of exhaust gases recirculated to the intake manifold of the engine to an optimum value which is determined in accordance with opening conditions of the engine carburetor throttle valve. Another expedient proposed in the prior art is to provide a flow restriction or orifice in the exhaust gas recirculation passage connected to the intake manifold of the engine. With this construction, the flow of the exhaust gases recirculated to the intake manifold increases as the intake manifold vacuum increases, viz., with the decrease in opening degrees of the engine carburetor throttle valve and vice versa. Thus, when the intake manifold vacuum is at high level, the exhaust gases are recirculated to the intake manifold in an excessive amount so that the engine power output is inevitably decreased.

It is, therefore, an object of the present invention to provide an improved flow control device for an exhaust gas recirculation system of an internal combustion engine.

Another object of the present invention is to provide a flow control device for an exhaust gas recirculation system of an internal combustion engine, which device is adapted to control the amount of exhaust gases recirculated to an intake manifold of the engine to a valve optimum for reducing the toxic nitrogen oxides contained in the exhaust gases.

Another object of the present invention is to provide a flow control device for an exhaust gas recirculation system of an internal combustion engine, which device is adapted to control the amount of exhaust gases recirculated to an intake manifold of the engine in accordance with the opening degree of a carburetor throttle valve of the engine.

Still another object of the present invention is to provide a flow control device for an exhaust gas recirculation system of an internal combustion engine, which device is capable of controlling the amount of exhaust gases recirculated to an intake manifold of the engine to an optimum value in accordance with opening degree of a carburetor throttle valve of the engine.

A further object of the present invention is to provide a flow control device for an exhaust gas recirculation system of an internal combustion engine, which device is simple in construction and economical to manufacture.

These and other objects and advantages of the present invention will become more apparent form the following description when taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a graph illustrating the relationship between the opening degree of a carburetor throttle valve and the amount of exhaust recirculation;

Fig. 2 is a schematic sectional view of a preferred embodiment of the flow control device according to the present invention; and

FIG. 3 is a view showing a modified form of the flow control device shown in FIG. 2.

Referring now FIG. 1, there is shown a graph illustrating variations in the amount of exhaust recirculation in terms of the opening degree of a carburetor throttle valve of the engine. In FIG. 1, curve X represents the amounts of exhaust recirculation which are desirable to control the nitrogen oxide concentration in the exhaust gases. As shown, the curve X is mountain-shaped and has a maximum point at a given opening degree A.sub.1 of the carburetor throttle valve. Curves Y.sub.1 and Y.sub.2 indicate the amounts of exhaust recirculation, which are obtained in the event that flow control valves are located in the exhaust gas recirculation passages, respectively through the use of prior art devices. Each of these flow control valves is of the type which cooperates with the carburetor throttle valve for varying the effective cross sectional area through which the exhaust gases flow and which is adapted to increase the effective cross sectional area of the exhaust recirculation passage with the increase in the opening degree of the carburetor throttle valve until the opening degree of the carburetor throttle valve reaches approximately the point A.sub.2 or A.sub.3 and thereafter to decrease the effective cross sectional area of the exhaust recurculation passage. Accordingly, it is quite difficult for the flow control valve to vary the amount of exhaust recirculation so as to approximate the curve X. If, for example, the flow control valve is arranged to vary the amount of exhaust recirculation so as to approximate the curve X in the range of lower opening degree of the carburetor throttle valve as shown by the curve Y.sub.1, then the amount of exhaust recirculation will be excessively increased in the range of higher opening degree of the carburetor throttle valve. If, on the contrary, the flow control valve is arranged to vary the amount of exhaust recirculation so as to approximate the curve X in the range of higher opening degree of the carburetor throttle valve, then the amount of exhaust recirculation will be insufficient in the range of lower opening degree of the carburetor throttle valve. Thus, an additional cam mechanism is required in the prior art exhaust gas recirculation control system for varying the amount of exhaust recirculation in a manner approximate to the curve X shown in FIG. 1.

In FIG. 1, curve Z represents variations in the amount of exhaust recirculation in the event that a flow restriction or orifice is located in the exhaust recirculation passage. Since the exhaust recirculation passage is arranged to communicate with the intake manifold of the engine, the amount of exhaust recirculation admitted through the flow restriction tends to increase as the intake manifold vacuum increases, viz., when the opening degree of the carburetor throttle valve decreases. Thus, it appears that the curve Z falls with the increase in the opening degree of the carburetor throttle valve. Therefore, the amount of exhaust recirculation can be varied so as to approximate the curve X in the range of higher opening degree of the carburetor throttle valve by properly calibrating the effective cross sectional area of the flow restriction. In the range of lower opening area of the carburetor throttle valve, the intake manifold vacuum is so high that the amount of exhaust recirculation increases abruptly and, during this particular range, the exhaust recirculation passage should be shut off.

In order to overcome the shortcomings mentioned hereinabove, the present invention contemplates to provide an improved flow control device for use in an exhaust recirculation system of an internal combustion engine which device is capable of varying the amount of exhaust recirculation to a valve approximating the curve X.

Referring now to FIG. 2, there is shown in section a preferred embodiment of the flow control device implementing the present invention. The flow control device proposed by the present invention is specifically suited for use in the exhaust gas recirculation system of an internal combustion engine. The internal combustion engine generally includes, as customary, a carburetor 10 having a throttle valve 12 mounted therein, an intake manifold 14 connected to the carburetor 10 and an exhaust manifold (now shown) through which engine exhaust gases are emitted. As shown, the throttle valve 12 is rotatably mounted on a rotary shaft 12a.

The flow control device, which is generally designated by reference numeral 16, has a casing 18 in which a passageway 20 is formed. The passageway 20 forms a part of an exhaust gas recirculation passage and communicates with the exhaust manifold (now shown) of the engine for recirculating a portion of the engine exhaust gases emitted therefrom to the intake manifold 14 of the engine.

To control the amount of exhaust gases recirculated through the exhaust gas recirculation passage, a butterfly valve 22 is disposed in the passageway 20. The butterfly valve 22 is rotatably mounted on a rotary shaft 22a so as to be rotatably for thereby varying the effective cross sectional area of the passageway 20.

The rotary shaft 22a of the butterfly valve 22 is linked with the rotary shaft 12a of the carburetor throttle valve 12 through a mechanical linkage 24. The mechanical linkage 24 is shown as comprising a first arm 26 having its one end connected to the rotary shaft 22a of the butterfly valve 22, connecting rod 28 having its one end connected to the other end of the first arm 26, and a second arm 30 having its one end connected to the other end of the connecting rod 28 and having its other end connected to the rotary shaft 12a of the carburetor throttle valve 12. Thus, the butterfly valve 22 is opened and closed in dependence on the opening condition of the carburetor throttle valve 12.

The butterfly valve 22 is so arranged as to be closed when the carburetor throttle valve 12 is substantially closed as shown in FIG. 2 whereas when the carburetor throttle valve 12 is rotated counter-clockwise as viewed in FIG. 2 by an acceleration control member (not shown), the rotary shaft 22a of the butterfly valve 22 is rotated clockwise through the mechanical linkage 24 thereby opening the butterfly valve 22 in dependence on the opening degree of the carburetor throttle valve 12 to vary the amount of the engine exhaust gases E passing through the passageway 20. It should be noted that the cross sectional area of the passageway 20, respective lengths of the first and second arms 26 and 30 and mounting angles of the first and second arms 26 and 30 relative to the rotary shafts 22a and 12a are so determined as to cause the butterfly valve 22 to vary the amount of the exhaust gases passing through the passageway 20 in a manner as shown by the curve Y.sub.1 of the graph of FIG. 1, viz., to a value which approximates the curve X in FIG. 1 in the range of O - A.sub.1 of the throttle opening.

Another important feature of the present invention resides in the provision of a flow restriction 32 which is located in the exhaust gas recirculation passage downstream of the butterfly valve 22. In the illustrated embodiment of FIG. 2, the flow restriction 32 is shown as consisting of an annular plate 34 having formed therein a restricted opening 34a communicating with the passageway 20. The flow restriction 32 is located in an annular recess 36a formed in an additional casing 36, which is fixedly connected through a gasket 38 to the casing 18 by suitable fastener means 40. As shown, the additional casing 36 is also formed with a passageway 42 which is aligned with the passageway 20 of the casing 18 to communicate therewith. The passageway 42 also forms a part of the exhaust gas recirculation passage and communicates with the intake manifold 14 of the engine, though not shown. It should be understood that the effective cross sectional area of the restricted opening 34a is calibrated to be such as to vary the amount of the exhaust gases recirculated through the exhaust gas recirculation passage in a manner approximate to the curve X in FIG. 1, viz., in a manner as shown by the curve Z in FIG. 1 when the throttle opening exceeds the level of A.sub.1 in FIG. 1. Thus, the combination butterfly valve 22 and flow restriction 32 provided in series with each other provides an advantage in that the amount of exhaust recirculation is controlling in a manner as shown by dotted lines O-C-B which approximates the curve X in FIG. 1.

The flow control device 16 may further comprise a second butterfly valve 44 serving as a flow shut off valve which is located in the passageway 20 downstream of the butterfly valve 22 for closing the passageway 20 during cold starting of the engine or when the content of nitrogen oxides is small such as during light load operation of the engine. The flow shut off valve 44 is rotatably mounted on a rotary shaft 44a, to which an arm 46 is fixed. The arm 46 is connected at its one end through a connecting rod 48 to an actuator 50. The actuator 50 may be of type having a diaphragm which is responsive to intake manifold vacuum of the engine and which is fixedly connected to the rod 48 for rotating the arm 46. To this end, the actuator 50 communicates through a conduit 52 with the intake manifold 14 of the engine. Indicated at 54 is a solenoid valve which is disposed in the conduit 52 for opening and closing the same. This solenoid valve 54 is arranged to be energized for opening the conduit 52 in response to a signal S indicative of cold operating condition of the engine or of light load operating condition of the engine. As the solenoid valve 54 is energized, the conduit 52 is opened so that the intake manifold vacuum is delivered to the actuator 50. Then, the actuator 50 operates to cause the rod 48 to move downwardly thereby rotating the arm 46 and accordingly the rotaty shaft 44a counterclockwise. Thus, the flow shut off butterfly valve 44 is rotated in a direction to close the passageway 20 and, therefore, the flow of exhaust gases is shut off.

In the flow control device 16 thus mentioned hereinabove, the second butterfly valve 44 may be so arranged as to be maintained at its slightly opened condition for thereby providing throttle effect even in the event that the engine is operating under the load or under cold condition and, thus, the annular plate 34 can be dispensed with. To this end, suitable means such as a stop (not shown) can be provided as a means for limiting the rotation of the arm 46 and accordingly the opening angle of the second butterfly valve 44. Thus, in the case where the second butterfly valve is arranged to provide the throttle effect, the opening angle of the second butterfly valve can be small and, therefore, the second butterfly valve can be actuated by an electro-magnetic solenoid instead of the actuator 50 mentioned hereinabove. One preferred example carrying out this concept is illustrated in FIG. 3, wherein like or corresponding component parts are designated by same reference numerals.

In the modified form of the flow control device 16 shown in FIG. 3, the second butterfly valve 44 has functions not only to completely shut off the passageway 20 during light load operating condition and cold operating condition of the engine but also to restrict the flow of exhaust gases passing through the passageway 20 when it is opened. The rotary shaft 44a of the second butterfly valve 44 is secured to an arm 56 having its lower end 56a biased by a tension spring 58 suspended from a flange 60 secured to the casing 18 so that the second butterfly valve 44 is moved in a direction to close the passageway 20. The lower end 56a of the arm 56 is made of a piece of iron and spaced from an opposing end of a magnetic core 62a of an electro-magnetic solenoid 62 by a distance l. The electro-magnetic solenoid 62 is electrically connected to a control unit 64 and controlled thereby in response to the signal S which has been previously mentioned. When the signal S is applied to the control unit 64, the electro-magnetic solenoid 62 is de-energized so that the arm 56 is rotated clockwise by the action of the tension spring 58 and, accordingly, the second butterfly valve 44 is maintained in its closed condition. If the signal S disappears, then the control unit 64 energizes the electro-magnetic solenoid 62 so that the magnetic core 62a attracts the lower end 56a of the arm against the action of the tension spring 58. In this condition, the arm 56 is rotated counterclockwise thereby opening the second butterfly valve 44 to a given opening degree determined by the distance l. It should be understood that the opening degree of the second butterfly valve 44 can be suitably determined by selecting the distance l between the lower end 56a of the arm and the magnetic core 62a whereby an optimum throttle effect is obtained to vary the amount of exhaust recirculation as shown by the curve X in FIG. 1.

It will now be appreciated from the foregoing description that the flow control device of the present invention is capable of controlling the amount of exhaust recirculation in a manner optimum for reducing the content of the toxic nitrogen oxides in engine exhaust gases without impairing engine operation.

It will also be noted that the flow control device of the present invention is constituted by a minimum number of component parts to provide a simple construction which is readily assembled and economical to manufacture.

Claims

What is claimed is:

1. In an exhaust gas recirculation system of an internal combustion engine having a carburetor throttle valve and an intake manifold, a flow control device for controlling the amount of exhaust recirculation to said intake manifold, said device comprising, in combination, passage means for recirculating engine exhaust gases to said intale manifold, valve means disposed in said passage means and responsive to the opening degree of said throttle valve for varying the effective cross sectional area of said passage means, and flow restricting means located in said passage means in series with, and downstream of said valve means, said flow restricting means including a butterfly valve downstream of said valve means, a diaphragm type actuator responsive to intake manifold vacuum, a butterfly valve arm linked to said actuator, a passageway connecting said intake manifold to said actuator, a solenoid valve located in said passageway in response to a signal indicative of said engine operating under light load and cold condition causing said actuator to close said butterfly valve through movement of said throttle valve arm linked to said actuator.

2. In an exhaust gas recirculation system for an internal combustion engine having a carburetor throttle valve and an intake manifold, a flow control device for controlling the amount of exhaust recirculation to said intake manifold, said device comprising, in combination, passage means for recirculating engine exhaust gases to said intake manifold, valve means disposed in said passage means for controlling the effective cross sectional area of said passage means, a mechanical linkage interconnecting said valve means to said carburetor throttle valve for thereby causing said valve means to open and close said passage means in dependence on the position of said carburetor throttle valve, and flow restricting means located in said passage means in series with, and downstream of said valve means, said flow restricting means including a butterfly valve downstream of said valve means, a diaphragm type actuator responsive to intake manifold vacuum, a butterfly valve arm linked to said actuator, a passageway connecting said intake manifold to said actuator, a solenoid valve located in said passageway to close said passageway in response to a signal indicative of said engine operating under light load and cold condition causing said actuator to close said butterfly valve through movement of said butterfly arm linked to said actuator.

3. A flow control device according to claim 2, in which said mechanical linkage includes a first arm secured to said valve means, a connecting rod connected at its one end to said first arm, and a second arm secured to said carburetor throttle valve and connected to the other end of said connecting rod.