Exhaust Gas Recirculation

Abstract

In an internal combustion engine equipped with an air valve carburetor, exhaust gases are recirculated through a vacuum operated valve to a port in the carburetor mixture conduit disposed adjacent and traversed by the upstream edge of the air valve. A tube mounted in the carburetor throttle body and air horn castings is utilized to recirculate the exhaust gas to minimize heat transfer to the carburetor.

Description

This invention relates to the recirculation of exhaust gases, from exhaust system to induction system in an internal combustion engine.

It has been recognized in recent years that recirculation of exhaust gases is an effective method of reducing formation and emission of oxides of nitrogen in internal combustion engines. In practice, it is desired to control the rate of flow of exhaust gases into the induction system in proportion to the rate of flow of combustion air through the induction system.

Several recent proposals for controlling exhaust gas recirculation have made use of the fact that exhaust gases flow into a region of constant pressure at a rate generally proportional to the rate of combustion air flow to the engine. Thus systems have been proposed for recirculating exhaust gases to a carburetor air cleaner, to a carburetor mixture conduit between the venturi and the throttle, and to a constant pressure region created in a recirculation passage extending directly from an exhaust passage to the intake manifold below the carburetor throttle.

The exhaust gas recirculation system shown herein also delivers exhaust gases to a constant pressure region in the engine induction system to thereby provide recirculation at a rate proportional to the induction air flow rate. However, this system differs from prior systems by delivering exhaust gases to the constant pressure region created in an air valve carburetor downstream of the air valve.

An important feature of this system is the use of a discharge port, opening from the exhaust gas recirculation passage into the carburetor mixture conduit or induction passage, which is traversed by the edge of the air valve during opening movement of the air valve. This permits the proportion of exhaust gas flow to air flow to be minimized when the air valve is closed and increased to a selected value as the air valve opens.

Another feature shown herein, which also may have utility in other carburetors, is an exhaust gas recirculation tube separate from the carburetor castings. It generally is contemplated that exhaust gas recirculation passages will be cast integrally in the manifold structure. The exhaust gases thus may be brought to the carburetor without piping external to the main engine structure. The exhaust gas recirculation tube receives exhaust gases in the throttle body casting at the base of the carburetor, bypasses the fuel bowl casting, and delivers the exhaust gases to the air horn casting for discharge adjacent the edge of the air valve. This construction avoids undue heat transfer from the exhaust gases to the fuel in the carburetor. In addition, the tube is mounted during carburetor assembly and is completely incorporated therein.

The details as well as other objects and advantages of this invention are set forth in the remainder of the specification and are shown in the drawings in which:

FIG. 1 is a sectional elevational view of the carburetor showing the basic metering linkage;

FIGS. 2 and 3 are enlarged views of the metering rod showing the configuration of the tapered portions; and

FIG. 4 is a side elevational view of the carburetor, manifold, and exhaust gas recirculation system with parts broken away to illustrate details of construction.

Referring first to FIG. 1, the carburetor 10 has a mixture conduit or induction passage 12 including an air inlet 14 and a mixture outlet 16 which discharges to the engine. A throttle 18 is disposed in mixture outlet 16 in the usual manner on a throttle shaft 20.

An air valve 22 is disposed in air inlet 14 on an air valve shaft 24. A spring 26 is hooked over the downstream edge 28 of air valve 22 and extends to a bracket 30 to bias air valve 22 to the position shown.

A tang 32 reaches upwardly from air valve 22 and is connected by a link 34 to a diaphragm 36. A chamber 38, formed between the right side of diaphragm 36 and a cover member 40, is connected by a tube 42 to a region 44 of mixture conduit 12 defined between air valve 22 and throttle 18.

A chamber 46, defined between the left side of diaphragm 36 and a cover member 48, is subjected to substantially atmospheric pressure, present in air inlet 14 and in the air cleaner (not shown), through openings such as 50, 52 and 54. (The air cleaner seats on a rim 56 disposed about the upper portion of carburetor 10).

In operation, chamber 38 is subjected to the subatmospheric pressure created in region 44 as throttle 18 is opened, and diaphragm 36 acts through link 34 to pull air valve 22 clockwise to an open position. Spring 26 is effective to balance the opening force of diaphragm 36, thereby creating a substantially constant subatmospheric pressure in region 44. By thus establishing a generally constant pressure drop across air valve 22, the area about air valve 22 and thus the rotative position of air valve 22 is determined by and is a measure of the rate of air flow through mixture conduit 12.

A tab 58 extends upwardly from air valve 22 and is connected through a link 60 to one end 62 of a lever 64. The opposite end 66 of lever 64 is pivoted about a pin 68. Intermediate ends 62 and 66, a hanger 70 extends from lever 64 into the carburetor fuel bowl 72. The lower end 74 of hanger 70 has a hook 76 which is received in a recess 78 formed in a metering rod 80.

It may be noted that hanger 70 extends through an opening 82 in the cover 84 for fuel bowl 72. Opening 82 is closed by a slider 86 which shifts horizontally during movement of hanger 70.

Metering rod 80 is disposed in a fuel passage 88 having its lower end 90 disposed to receive fuel from a well 92 formed in the bottom of fuel bowl 72. The upper end 94 of fuel passage 88 has an opening 96 through which fuel is discharged into region 44 of mixture conduit 12. It wil be appreciated, therefore, that the fuel bowl 72 is subjected to a substantially constant metering head -- from the substantially atmospheric pressure in the upper portion of the fuel bowl to the generally constant pressure in region 44.

A metering jet or orifice 98 is disposed in fuel passage 88 around the tip 99 of metering rod 80. As best shown in FIGS. 2 and 3, metering rod 80 has flat tapered surfaces 100 on opposite sides which, upon reciprocation of metering rod 80 is jet 98, varies the area available for fuel flow through jet 98.

In operation, as air valve 22 opens by clockwise rotation, link 60 rotates lever 64 in a clockwise direction. Lever 64 then lifts hanger 70 to move metering rod 80 generally upwardly and righwardly in fuel passage 88. Thus as air valve 22 is opened to increase the area available for air flow through air inlet 14, metering rod 80 is shifted to increase the area available for fuel flow through metering orifice 98. By this means, a substantially constant air-fuel ratio may be maintained -- the precise proportion being controlled by the geometry of tapered surfaces 100 and of the linkage between air valve 22 and metering rod 80.

A spring 102 extends from an annular ledge 104 formed in fuel passage 88 to the lower end 106 of metering rod 80 to take up any slack in the linkage and to load metering rod 80 against jet 98.

It may be noted from FIG. 3 that the thickness of metering rod 80 increases from the end of surfaces 100 most closely adjacent passage inlet 90 to tip 99. Tip 99 is therefore enlarged and assists in discharging fuel from fuel passage 88 as air valve 22 and metering rod 80 are moved to increase air and fuel flow. This offsets the greater inertia of the fuel which otherwise could create a mixture temporarily leaner than desired.

Referring now to FIG. 4, it may be noted that carburetor 10 includes a throttle body casting 111, a fuel bowl casting 113 separated from throttle body 111 by a thick gasket 115, and an air horn casting 117 separated from fuel bowl casting 113 by a gasket 119. Carburetor 10 is mounted on an intake manifold 121 which has a riser bore 123 in registration with mixture outlet 16 and a plurality of passages 125 extending to the engine combustion chambers.

An exhaust heat passage 127 is incorporated in manifold 121 below riser bore 123 and receives a portion of the exhaust gases discharged from the engine combustion chambers.

An exhaust gas recirculation pasage 129, 131 extends through the manifold casting from exhaust heat passage 127 to a control valve assembly 133 and from control valve assembly 133 to carburetor throttle body 111. The lower end of an exhaust gas recirculation tube 135 is received in a bore 137 in throttle body 111 and registers with recirculation passage 131. The upper end of the tube 135 is received in a bore 139 in air horn 117 and registers with a passage 141 formed in air horn 117. Passage 141 extends to a port 143 disposed in air inlet 14 just above the upstream edge 145 of air valve 22.

Control valve assembly 133 comprises a valve body 147 having an inlet 149 in registration with recirculation passage 129 and an outlet 151 in registration with recirculation passage 131. A valve pintle 153 controls flow through inlet 149 and is connected by a stem 155 to a diaphragm 157. The chamber 159 enclosed above diaphragm 157 is subjected through a tube 161 to the pressure at a port 163 disposed in mixture conduit 12 just above the upstream edge 165 of throttle 18. The lower side of diaphragm 157 is exposed to atmospheric pressure.

In operation, a throttle 18 is opened, its upstream edge 165 traverses port 163, and chamber 159 is subjected to the manifold vacuum downstream of throttle 18. Diaphragm 157 then overcomes spring 167 and displaces pintle 153 from inlet 149 to permit recirculation of exhaust gases from exhaust heat passage 127 through recirculation passage 129, valve body 127, recirculation passage 131, tube 135, passage 141, and port 143 to mixture conduit 12. Until the upstream edge 145 of air valve 22 reaches port 143, the exhaust gases are recirculated into the substantially atmospheric pressure in air inlet 14 in proportion to engine induction air flow.

As air valve 22 opens in response to increased air flow, upstream edge 145 traverses port 143 to subject port 143 to the substantially constant subatmospheric pressure in region 44. This reduction in pressure at port 143 increases the proportion of exhaust gas flow to air flow.

The location of port 163 with respect to throttle 18 will determine the cut-in point for actuating valve assembly 133 to initiate recirculation of exhaust gases, and the location of port 143 with respect to air valve 22 will determine the point at which the proportion of exhaust gas flow to air flow is increased.

It will be appreciated that while valve assembly 133 is described here as an on-off control, port 163 may be contoured and valve assembly 133 designed to provide an exhaust gas metering function.

It also will be appreciated that the configuration of port 143 will determine the rate of transition from the minimum proportion of exhaust gas flow when air valve 22 is closed to the selected proportion of exhaust gas flow when air valve 22 is open.

Tube 135 serves an important function in minimizing heat transfer to the fuel within fuel bowl 72. If exhaust gases were recirculated through passages cast in throttle body 111, fuel bowl section 113, and air horn 117, heat conduction to the fuel in fuel bowl 72 would be substantial. By recirculating exhaust gases through the separate tube 135, connected only at the ends to throttle body 111 and air horn 117 and completely bypassing fuel bowl section 113, such heat conduction is minimized.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An internal combustion engine comprising an induction passage for air flow to the engine, an air valve disposed in said induction passage and rotatable between closed and open positions, means controlling said air valve to maintain a substantially constant pressure in a region of said induction passage downstream from said air valve, an exhaust passage for exhaust gas flow from the engine, and an exhaust gas recirculation passage extending from said exhaust passage to a port disposed in said induction passage adjacent the upstream edge of said air valve when said air valve is in said closed position and traversed by the upstream edge of said air valve as said air valve is rotated from said closed position to said open position whereby when said air valve is in said open position exhaust gases are recirculated into a region of substantially constant pressure in said induction passage to thereby provide recirculation of exhaust gases at a rate proportional to the rate of air flow, and whereby the proportion of exhaust gas flow to air flow may be increased from a minimum when said air valve is in said closed position to a selected value as the upstream edge of said air valve traverses said port.

2. The engine of claim 1 which further comprises a throttle disposed in said induction passage downstream of said air valve and rotatable between closed and wide open positions for controlling air flow therethrough, valve means disposed in said recirculation passage for preventing the flow of exhaust gases therethrough, a diaphragm connected to said valve member, and means for subjecting said diaphragm to the pressure at a port disposed in said induction passage adjacent the upstream edge of said throttle when said throttle is in said closed position and traversed by the upstream edge of said throttle as said throttle is rotated from said closed position, whereby said diaphragm may position said valve member to prevent the flow of exhaust gases through said recirculation passage when said throttle is in said closed and wide open positions and to permit the flow of exhaust gases through said recirculation passage when said throttle is intermediate said closed and wide open positions.