Egr Enrichment Valve

Abstract

An internal combustion engine is disclosed having an exhaust gas recirculation system effective to return exhaust gases to the intake manifold. The carburetion system for the engine is arranged to compensate for the recycling of exhaust gases by the use of in-series fuel enrichment valves subject to the same limiter, the first being effective to introduce supplementary fuel in response to an increase in ported advance vacuum taken from the carburetor and the second adding fuel during wide-open throttle conditions in response to the dissipation of manifold vacuum.

Description

BACKGROUND OF THE INVENTION

The carburetion system of an internal combustion engine is designed to supply to the cylinders a combustible mixture with an air-fuel ratio predetermined to provide the best engine performance for economy. The engine designer has to consider the carburetor and the intake manifold as an integral system. Because of the transient flow phenomena occurring in the manifold as well as the heterogeneity of the combustible mixture delivered by the carburetor, there is imposed quite narrow limits to the range of air-fuel ratios which will provide satisfactory engine operation. Unfortunately, the range of air-fuel ratios which give best engine performance do not coincide with that which results in a minimum emission of contaminants from the engine exhaust system. A minimum emission from all exhaust contaminants results when the engine operates with about 20-30 percent excess of air. This is above the lean limit of satisfactory operation of an engine equipped with a conventional carburetor. Therefore, most engine designers have attempted to use exhaust gas recycling in a manner to inject recirculation only at times when the engine can best handle the leaner mixtures without sacrificing drivability. Unfortunately, this approach has met with only compromised success for two reasons: (a) greater reduction in the NO.sub.x emissions from present recycling must be obtained if future Federal Standards are to be met, and (b) the engines with present exhaust gas recycling encounter an unstable condition commonly called "power surging."

As to the need for a greater decrease in NO.sub.x emissions while recycling, it should be understood that reduction of NO.sub.x compounds results directly from a reduction in the combustion temperature of the combustible mixture. The amount of nitric oxide produced in the engine cylinder from atmospheric nitrogen and oxygen is an exponential function of the combustion temperature, therefore even a moderate decrease in the combustion temperature will result in a decrease in nitric oxide production. In some tests, a 15 percent exhaust recycling produced a reduction of nitrogen oxides by about 88 percent, power output was reduced by about 16 percent and economy reduced by about 14 percent. Power loss and reduced economy can be balanced by change of spark timing. In another test using a spark advance of 19.degree., the power and economy drop was compensated, but nitrogen oxide emissions increased considerably. Thus, at balanced power, there was only about a 60 percent reduction. With the present invention, it is contemplated that NO.sub.x emissions can be reduced to as much as 90 percent or above.

Turning to the phenomenon "power surging," this effect is most notable at around 50 miles per hour cruising speed and at about 15 inches of mercury of manifold vacuum when the rate of exhaust recycling is high. Since the exhaust recycled into the inlet manifold is introduced below the carburetor, the air-fuel ratio, or rather oxygen-fuel ratio remains unaffected. However, the ratio of total gas flow (air plus exhaust) to fuel flow is increased. For example, the carburetor of a typical test car at 50 miles per hour delivers a mixture at an air-fuel ratio of 14.0:1. Recycling of about 18 percent of exhaust gas represents the addition of about 2.6 lbs. of gases, which brings the total gas-fuel ratio to 16.6:1 and results in heavy surge. It can be seen that there is a need for balancing the total gas-fuel ratio by increasing the fuel flow during recycling so as to obtain the original ratio of 14:1 to eliminate power surging.

SUMMARY OF THE INVENTION

The primary object of this invention is to provide a carburetion system for an internal combustion employing exhaust recirculation and which is capable of eliminating power surging effects due to recirculation and which can reduce NO.sub.x emissions to even greater levels than that achieved by current exhaust gas recirculation.

Another object is to provide a carburetion system effective to operate with exhaust gas recirculation and provide additional fuel during such recirculation. The additional fuel should be limited in some manner by a simplified control.

Yet another object of this invention is to provide a carburetion system that not only decreases power surging effects resulting from exhaust gas recirculation, but provides such decrease in a stable manner by using fuel enrichment means in conjunction with a carburetor which introduces primary fuel through a booster venturi. The atomization of the increased fuel flow through annular arranged openings in said booster venturi provides such stabilization.

One feature of this invention is the provision of an enrichment valve which is normally biased to an open position by a vacuum signal obtained from the carburetor system and closed by a predetermined resilient force when said vacuum signal subsides particularly when exhaust gas recirculation is interrupted.

DETAILED DESCRIPTION

Turning now to the preferred embodiment as illustrated in FIG. 1, an engine A is provided having a conventional intake system B with a carburetor C and a conventional exhaust system D. An exhaust gas recirculating system E returns a part of the exhaust gases for recycling to achieve lower emission levels. The carburetor C has a fuel system F which employs two enrichment valves G and H for supplying supplementary fuel, over and above the normal primary fuel system.

Turning now in more particularity to the components, the carburetor C is generally of three-piece construction having an air horn section 10 within which is disposed a usual choke 10a, a main body section 11 containing a main venturi restriction 12 and an integral cast booster venturi 13 carried by supporting arms 14 extending integrally to the body section 11. A throttle body section 17 contains a suitably journalled throttle plate 18, effective to be moved between a position where the intake system is substantially closed and a wide-open throttle position which offers the least resistance to flow therethrough. The booster venturi has an internal wall 15 and a full ring of inducting ports 16 in said wall; each port 16 is in communication with a suitable passage for carrying fuel thereto as will be described.

The fuel system F comprises a fuel reservoir 20 in which is maintained fuel to a predetermined level by suitable controls (not shown). A main jet (not shown) communicates reservoir 20 with a main uptake passage 21 connecting with another passage 22 extending through the integral casting arm 14. Fuel from the reservoir is drawn through the jet passages 21 and 22, and openings 16 by a vacuum created from air passing through the booster and main venturies. The amount of vacuum is determined by the air flow therethrough which in turn is regulated by the load on the engine. The difference in pressure between the main discharge ports 16 and the fuel reservoir, causes fuel to flow as indicated. As fuel moves through the passage 21, air from the bleed passage 23 enters the fuel flow. The bleed meters an increasing amount of air to the fuel as venturi vacuum increases maintaining the required fuel-air ratio. The mixture of fuel and air is lighter than raw fuel and responds faster to changes of venturi vacuum. It also vaporizes more readily than raw fuel. Fuel and air thus continue through passage 22 and out through all openings 16 in an annular spray pattern.

During periods of increased road loads or high speed operation, added fuel is required and is supplied by the supplementary fuel means G. Means G comprises a fuel orifice or seat 24 defined as a conical surface on element 25 threadably inserted in the base of the fuel reservoir. Element 25 has passages 25a and 25b providing an inlet and outlet to the valve orifice 24. A central opening 25c journals to valve stem 26 which in turn carries a valve 27 at the base thereof. The valve 27 has a conical surface 27a which is adapted to mate with the surface 24. Stem 26 extends upwardly through reservoir 20 and carries a piston 28 at the upper end adapted for intimate sliding engagement with a passage 29. A suitable retainer 30 is mounted at the upper portion of the reservoir to assist in journalling the stem 26. The upper face 28a of the piston is subjected to the pressure that resides in the upper portion of passage 29, the latter communicating with a port 31 disposed downstream of the throttle 18 in its closed position; port 31 communicates with intake manifold vacuum.

Due to recent federal regulations controlling emission levels, current models of vehicles are equipped with exhaust gas recirculation. A typical system for accomplishing such recirculation comprises a duct 35 connecting a portion of the exhaust manifold directly with the intake manifold at a location immediately downstream of port 31. Interposed in duct 35 is an admitting means 36 having a valve 37 adapted to close off a portion of the duct 35. This is accomplished by forming the duct to communicate with a chamber 38 having an inlet and outlet thereto. Thus, the outlet 38a may be closed or opened by valve 37. Valve 37 is operated by a diaphragm assembly 39 consisting of a diaphragm 62 bisecting a chamber 40; the diaphragm is urged in one direction by a helical spring 41 adapted to maintain a predetermined force to urge the valve to a closed position. One side of the diaphragm is subjected to intake manifold vacuum so that under conditions of some intake manifold vacuum, the valve will be opened allowing exhaust gases to recirculate.

The addition of exhaust gas recirculation, downstream of the throttle, essentially leans out the air-fuel ratio because the greater gaseous flow downstream of the throttle. Flow through the primary venturi is reduced thereby resulting in a cutback in the induced metering of fuel. At certain cruising speeds, the engine may operate in an unstable way, commonly called "power surging." The severity of power surging depends on the rate of exhaust recycling.

To overcome these problems, fuel valve means H is employed to add additional quantities of fuel during conditions particularly when exhaust gas recirculation is taking place. Means H comprises a sleeve 45 integrally cast as part of the base of reservoir 20; sleeve 45 is internally threaded for receiving a valve structure 46 defining a valve seat or opening 47. A valve 48 is provided with a flange 49 on its upper section which is biased upwardly by a spring 50 to close the valve opening when the normal opening force is dissipated. Normally the spring force is overcome by a servo-mechanism 57 enclosed in housing 58 and having a chamber 59 therein. Diaphragm 60, on one side, which is subjected to absolute pressure or vacuum pressure in chamber 59; the chamber 59 is in communication by way of passage 42 with a port 61 which is commonly referred to as ported advance vacuum; it is obtained in advance of the throttle when in the closed position.

Claims

I claim:

1. In an engine having an exhaust manifold, an intake manifold and a system for inducting a mixture of air and fuel into said intake manifold having a carbureted mixture flow controlled by a throttle, and means for recirculating exhaust gases from said exhaust manifold back into said intake manifold, the combination comprising:

a. means for metring supplementary fuel to said induction system in response to the dissipation of the vacuum level in said intake manifold, and

b. secondary means for metering additional fuel to said induction system in response to an increase in the vacuum signal obtained from said system immediately adjacent and in advance of said throttle.

2. The combination as in claim 1, in which the secondary means for metering additional fuel comprises a fuel having an orifice normally exposed to the fuel reservoir of said induction system, resilient means for urging said valve to a normally closed position, and a diaphragm assembly communicating with the vacuum signal upstream from said throttle in a manner to overcome said resilient means for opening said valve in response to the advance vacuum obtained during cruising conditions of the engine.

3. The combination as in claim 1, in which the secondary means for metering additional fuel has a restriction to limit the maximum flow of fuel to said intake manifold.

4. For use with an internal combustion engine having a manifold subject to engine intake vacuum, means for recirculating engine exhaust gases back to said manifold, a control operated by vacuum responsive regulator for admitting said recirculation, and carburetion means having a throttle and a first port subject to vacuum slightly in advance of said throttle and a second port subject to vacuum downstream of said throttle, the combination comprising:

a. means defining first and second fuel valves each calibrated independently for effecting supplementary addition of fuel to said carburetion means under predetermined conditions,

b. means effective to communicate said first port with said first fuel valve for actuation thereof in response to a first predetermined range of engine conditions, and

c. means effective to communicate said second port with said second fuel valve for actuation thereof in response to a predetermined range of engine conditions different then those for said first fuel valve.

5. The combintation as in claim 4 in which said carburetor has a booster venturi containing an internal channel for inducting fuel to the air flow through said booster venturi substantially about the annular interior thereof, said channel being in communication with said first and second fuel valves for providing induction of said fuel to said manifold.