Engine Exhaust Recirculation Apparatus

Abstract

An apparatus is provided for the recirculation of exhaust gases from an automobile's engine at a constant volume comprising a flow control valve in a passage for recirculating part of the engine exhaust gases into the engine's intake system.

Description

BACKGROUND OF THE INVENTION

This invention relates to a means for recirculating an engine's exhaust gas, and more particularly to an improved apparatus comprising a flow control valve adapted to maintain constant the volume of exhaust gas recycled into the intake system of an automobile or the like.

It is known that the amount of nitrogen oxides in automobile exhaust gases can be decresed by lowering the maximum combustion temperature of the air fuel mixture in cylinder. Among the known exhaust recirculation devices is one in which a part of the exhaust gases, most of which are inert gases, is mixed in the fuel-air mixture to increase its heat capacity to thereby reduce the combustion temperature. Most of the known flow control means used for controlling the exhaust recycling rate in such a device are composed substantially of a flap valve adapted to operate in response to the throttle valve in the carburetor such that as the throttle valve is turned 90.degree. to change from the full closed to the full open condition, the flap valve is turned 180.degree. to change from the full closed to the full open and then again to the full closed condition. The amount of exhaust gas which is recirculated varies with the total amount of engine exhaust gases during the above-said opening and closing operations as shown by curve a in FIG. 3.

On the other hand, it is known that other noxious substances, such as carbon monoxide, hydrocarbons, etc., ordinarily contained in exhaust gases can be decreased by using a lean mixture, but when the proportion of recycled exhaust gas to be mixed in the mixture varies in the above manner, the fuel-air ratio is also necessarily affected, and therefore even if a ratio for a lean mixture is regulated for coping with the noxious substances such as above-mentioned, half of its beneficial effect is lost.

SUMMARY OF THE INVENTION

The principal object of the present invention is to provide means for decreasing the content of nitrogen oxides in automobile exhaust gases. A more specific object of the invention is to provide an improved exhaust system for an automobile or the like having a device for recirculating a portion of the exhaust gas to the fuel intake pipe at a constant volume despite variation in volume of exhaust gas produced.

The foregoing objects and others are accomplished in accordance with this invention by providing an improved device for recirculating engine exhaust gases to the fuel intake system of an automobile or the like wherein a conduit communicating between the intake system and exhaust pipe is provided with a throttle and a diaphragm responsive to pressure on the downstream side of the throttle, and a control valve disposed downstream of said throttle and operated in response to said diaphragm to vary the sectional area of the recirculation passage, said control valve being adapted to control the sectional area of the recycle exhaust passage proportionally to the square root of the quotient of the pressure on the upstream side of said throttle and the pressure on the downstream side of said control valve.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 illustrates schematically, an engine and its exhaust recirculating system;

FIG. 2 illustrates in cross section an embodiment of the device provided by this invention for recirculating a portion of the exhaust gas to the fuel intake system of the engine of FIG. 1;

FIG. 3 compares diagrammatically the relationship between the amount of exhaust gas recirculated by a prior art device with that provided by the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

In FIG. 1 there is shown schematically an internal combustion engine having a conventional exhaust recirculation system including a by-pass exhaust recirculation system passage 4 provided between an exhaust pipe 2 and an intake pipe 3 both extending from an engine 1. A flow control means 10 is provided in accordance with the present invention in said passage 4. As is apparent from the detailed cross section of FIG. 2, the flow control means 10 of the present invention comprises a control valve 14 including a movable ball or similar member adapted to seat in the valve opening. Valve 14 is disposed in an orthogonally bent portion of the exhaust recirculation passage or conduit 4. Control valve 14 has a valve body 13 and a valve rod 12 slidably supported in a passage wall 4' and arranged in abuttable relationship against the valve seating member 11 in a direction opposite to the flow of exhaust gases being recirculated. A connecting member 15 integrally joined to the valve body 13 in its operative direction extends through the passage wall 4' to the outside of the passage.

In the passage 4 and upstream of said control valve 14 is also provided a throttle 16 in such a way as to define therebetween a control chamber 17. Connecting rod 15 is connected to a diaphragm 20 provided in a diaphragm assembly 18. A spring 19 is mounted on one side of diaphragm 20, and a pressure conduction pipe 22 connects the control chamber 17 to a pressure chamber 21 formed in the diaphragm assembly 18. A bellows 23 is secured at one end to member 13 and at the other end to passage wall 4' . Bellows 23 surrounds valve body 13 and is adapted to counteract the pressure acting on the backside face of the valve body. A second bellows 24 is provided at that part of the passage wall 4' where the connecting rod 15 passes to protect the sliding portion thereof from exhaust gases to keep it free from coagulation and other similar problems.

Because of the construction of the present system as described above, a part of the engine exhaust gases discharged through the exhaust pipe 2 is directed through passage 4 at a flow rate which is controlled by flow control means 10 into the intake pipe 3. When entering the flow control system 10, the flow rate of the exhaust gas is changed by throttle 16 according to its throttling area and then conducted into the control chamber 17. The gas under pressure in control chamber 17 is conducted through pipe 22 into pressure chamber 21 of the diaphragm assembly 18 where it acts upon the diaphragm 20, causing the connecting rod 15 and the valve body 13 to move against the biasing force of spring 19 in accordance with the pressure in chamber 21. Valve body 13 and valve seal 11 are thus opened to the extent dictated by the relative forces of the pressure in chamber 21 and the back pressure of spring 19 to thereby regulate the flow rate of exhaust gas recirculated into the intake pipe 3.

In the above-described flow controlling operation by the flow control system 10, if the amount of engine exhaust gas is increased to cause rise of pressure in the control chamber 17, the force acting on the diaphragm 20 is also correspondingly increased to enlarge the opening of the control valve 14 to thereby increase the exhaust gas flow rate into the intake pipe 3. On the contrary, if the amount of engine exhaust gas is decreased and pressure in the control chamber 17 is reduced, the opening of the control valve 14 is accordingly reduced to decrease the flow rate of exhaust gas into the intake pipe 3. In this manner, pressure in the control chamber 17 is maintained always at a constant level.

Because of the fact that exhaust gas from the exhaust pipe 2 is under positive pressure while the pressure on the downstream side of the control valve 14 is under the negative pressure of intake pipe, the pressure in the control chamber 17, which is kept at a constant value by changing the flow passage area of the control valve 14 in fixed relationship with the passage area of the throttle 16, pressure on the downstream side of the control valve 14 and pressure on the upstream side of the throttle 16, can be reduced substantially equal to atmospheric pressure, and therefore the amount of exhaust gas recirculated into the intake pipe 3 from the control valve 14 can be regulated at a value which is proportional to the square root of the pressure upstream of the throttle 16. On the other hand, the pressure upstream of the throttle 16 is substantially proportional to the square of the amount of engine exhaust gas, so that eventually the amount of exhaust recycling is rendered proportional to the amount of engine exhaust gas, and thus the ratio between them is fixed always at a constant value for any amount of engine exhaust gas, as shown by a straight line b in FIG. 3.

The exhaust recirculation control accomplished by the flow control system 10 as described above is now described by using mathematical expressions embodying the principles of the present invention.

Assuming that the intake pipe negative pressure is P.sub.1, exhaust pressure P.sub.E, control chamber pressure P.sub.C, flow passage area in throttle 16 F.sub.C, flow rate therethrough q.sub.1, flow passage area in control valve 14 F.sub.V, K.sub.1 and K.sub.2 are constants and flow rate therethrough q.sub.2, then the following formulae will hold:

q.sub.1 = k.sub.1 F.sub.C .sqroot.P.sub.E - P.sub.C

q.sub.2 = k.sub.2 F.sub.V .sqroot.P.sub.C - P.sub.I

From the above formulae, the following equation is given:

q.sub.1 /q.sub.2 = (k.sub.1 F.sub.C /K.sub.2 F.sub.V .sqroot.(P.sub.E - P.sub.C /P.sub.C - P.sub.I) = (k.sub.1 F.sub.C /k.sub.2 F.sub.V).sqroot.(1 - P.sub.C /P.sub.E /P.sub.C /P.sub.E - P.sub.I/P )

So, assuming that P.sub.C /P.sub.E = 0, or P.sub.C < P.sub.E, or P.sub.C = 0, the following equation is obtained:

q.sub.1 /q.sub.2 = (k.sub.1 F.sub.C /k.sub.2 F.sub.V).sqroot. - (P.sub.E /P.sub.I) = (k.sub.1 /k.sub.2) F.sub.C .sqroot. - (P.sub.E /P.sub.I).sup. . (1/F.sub.V)

Further assuming that the relationship of:

F.sub.V = (k.sub.1 / k.sub.2 )F.sub.C .sqroot. - (P.sub.E /P.sub.I)

is established, there is obtained the equation: q.sub.1 /q.sub.2 = 1. This gives:

q.sub.2 = q.sub.1 = k.sub.1 F.sub.C .sqroot. (P.sub.C - P.sub.I) [- (P.sub.E /P.sub.I)] = k.sub.1 F.sub.C .sqroot. P.sub.E - (P.sub.C P.sub.E /P.sub.I)

.apprxeq. k.sub.1 F.sub.C .sqroot. P.sub.E

The above formula dictates that the flow passage area controlled by the control valve 14 needs to be adjusted so that it is proportional to the square root of the quotient of the pressure on the upstream side of throttle 16 and the pressure on the downstream side of control valve 14, by suitably selecting the flow passage area of throttle 16, pressure-receiving area on the diaphragm, spring setting load, spring constant and other factors.

As described above, according to the flow control system of the present invention, the exhaust recycling rate is controlled so that the pressure just after the throttle in the exhaust recirculation passage connected between exhaust pipe 2 and intake pipe 3 of an engine 1 is kept at a fixed level, thereby to maintain always constant the rate of exhaust gas to be recirculated, regardless of the amount of engine exhaust gas. Therefore, even if the amount of engine exhaust gas is increased or decreased according to the automobile cruising conditions, the fuel-air ratio in the fuel supply system remains substantially unchanged, and hence the present device can be used for the above-said purpose without baffling the mixing ratio which has been set for decreasing the harmful components such as carbon monoxide, hydrocarbons, etc., in exhaust gases.

Although the invention has been described in detail for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations therein can be made by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims

What is claimed is:

1. An apparatus for recirculating exhaust gas from an exhaust pipe to an intake manifold comprising a conduit between the intake manifold and exhaust pipe, a throttle in the conduit, a valve in the conduit downstream of the throttle, said throttle and control valve defining a control chamber therebetween, a diaphragm, a rod connecting the diaphragm and valve, means for conducting gas from the control chamber against the diaphragm and thereby move the diaphragm and open the valve under the positive pressure in the control chamber, and a bellows between the valve and intake manifold urging the valve into its closed position to offset the effect of a negative pressure in the intake manifold.

2. In an exhaust system for an internal combustion engine provided with an intake manifold and an exhaust pipe, means for recirculating a part of the exhaust gas carried by the exhaust pipe to the intake manifold comprising a first conduit communicating between said intake manifold and said exhaust pipe, a throttle in said first conduit, a control valve in said first conduit downstream of the throttle and having a valve seat and a valve body adapted to seat in the valve seat, a valve rod secured to the downstream side of the valve body and slidably supported in said first conduit, a connecting rod secured at one end to the upstream side of the valve body and at its other end to a diaphragm, a housing enclosing the diaphragm and a chamber separated into two compartments by the diaphragm, a second conduit communicating at one end with said first conduit between the throttle and the valve seat and slidably connected at its other end with said housing and communicating with the compartment which is opposite the diaphragm from the valve body, and means for biasing the housing and diaphragm away from the valve seat, means for biasing said valve against the valve seat against the negative pressure of the intake manifold, whereby pressure in said first conduit between the throttle and valve seat is conducted through said second conduit into the compartment opposite the diaphragm from the valve seat and the diaphragm and said rod are moved against said biasing means in response to the pressure in said chamber.