Device For Regulating The Rate Of Flow Of Recycled Exhaust Gases In An Internal Combustion Engine

Abstract

In an internal combustion engine equipped with a mechanism for recycling the exhaust gases, or at least a fraction thereof to dilute the fresh mixture, the improvement consisting in providing means for sensing the pressure drop of the gases in the exhaust duct, means for sensing the pressure drop in the auxiliary duct intended for recycling the exhaust gases, and a member being provided for establishing a proportionality ratio between the respectively sensed pressure drops.

Description

BACKGROUND OF THE INVENTION

It is known that one of the methods which is being investigated in order to diminish the percentage of nitrogen oxides in the exhaust gases of internal combustion engines consists in diluting the charge of fresh mixture with burned gases taken from the exhaust duct. This expedient is an asset since, by so doing, the maximum temperatures of the ycle (their value influences the formation of nitrogen oxide) are decreased.

The amount of exhaust gas taken downstream of the engine in correspondence with the exhaust duct and suitably cooled, which is required, should be introduced upstream of the engine. In order to prevent deposits and fouling in the carburetor, in the engines equipped with a carburetor, it is advisable to effect this exhaust gas feed downstream of the carburetor, between the carburetor and the induction valve. However, as compared with the other approaches (such as the introduction of gases upstream of the carburetor), this solution involves a greater difficulty as regards the regulation of the amount of exhaust gas to be introduced; as a matter of fact, downstream of the carburetor and thus of the throttle, the pressure undergoes a considerable variation according to the conditions of use of the engine and the amount of exhaust gases tends to be extremely high when the throttle is partially closed under conditions of highly negative pressures whereas, on the contrary, it is very small when the throttle is fully open. This tendency is the exact contrary of what would be desirable: as a matter of fact, nitrogen oxides are formed in the explosion chamber prevailingly at high power deliveries whereas they are negligible when the engine is idling and delivers only reduced powers.

SUMMARY OF THE INVENTION

A first embodiment of the device according to the present invention has for its object to render the dilution ratio of the fresh mixture to the exhaust gases constant irrespective of the conditions of use of the engine in the operative range which is of interest; such an approach is, in fact, considered to be satisfactory as itself.

The device is based on the idea that, with a fair degree of approximation, if one maintains constant the ratio between the rate of flow of the exhaust gases introduced in the mixture (that is, recycled exhaust) and the overall rate of flow of exhaust gases, also the dilution ratio (that is, the ratio between the rate of flow of the recycled gas and the rate of flow of fresh mixture) remains constant. This idea is fully valid if the admixture ratio (intended as the ratio between the rate of flow of air and the rate of flow of fuel drawn by the engine) remains constant under the different conditions of use, but the variations of the admixture ratio are generally so slight as to have no determining bearing on a regulation carried out in this way.

An object of the present invention is to provide a particularly simple and reliable device for regulating the rate of flow of the recycled gases so that it may be in a substantially constant ratio with the rate of flow of the exhaust gases and thus, finally, with the rate of flow of the gases drawn by the engine.

According to the invention, an internal combustion engine, equipped with an intake duct, an exhaust duct and an auxiliary piping connected to said exhaust duct to draw a portion of the gases flowing therethrough to discharge them into said intake duct, is characterized in addition by first means sensitive to the pressure drop undergone by the gases flowing through at least a portion of said exhaust duct, by second means sensitive to the pressure drop undergone by the gases flowing through a portion of said auxiliary piping, and by a throttling member for said auxiliary piping which is driven to move by said first and said second means in the sense of keeping the sensed pressure drops proportional to each other, respectively.

It is well known that the pressure drops in a duct are proportional to the square power of the rate of flow (by volume) of the flowing fluid, and on the basis of said principle, the consequence is that the constancy of the ratio between the pressure drops sensed by said first and said second means, or their mere equality, ensures the constancy of the ratio between the respective rates of flow, in the exhaust duct and the recycle piping, according to the objects of the present invention.

The foregoing objects and features of the present invention can be better understood from the ensuing description of exemplary embodiments thereof as illustrated in the accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows as a diagrammatical overall view an internal combustion engine according to the invention,

FIG. 2 shows a cross-sectional view of a detail of FIG. 1, and

FIGS. 3 and 4 show modifications to the detail illustrated in FIG. 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In FIG. 1, the numeral 10 indicates an internal combustion engine having four in-line cylinders shown at 11, 12, 13, 14: the numeral 15 indicates the induction duct of the engine and 16 is the intake manifold from which branch off the individual intake ducts of the several cylinders. The numeral 17 indicates the body which contains the throttling members of the fluid drawn by the engine: a mixture in the case of an engine having a carburetor, and air in the case of an injection engine. The linkage mechanism of said throttling members, which is known as itself, is partly shown, with the accelerator pedal of the vehicle: the drawing shows a lever 18 connected to the throttling members and a rod 19 connected to an accelerator pedal (not shown). The numeral 20 indicates the filter, having also a silencing function for the air drawn from the outside by the engine. There are shown at 21, 22, 23, 24 the exhaust ducts coming from the individual cylinders and 25 is a manifold to which is flangedly connected at 26 a duct 27 which sends the gas to the outside.

In the duct 27 are arranged a postcombustion muffler 28 and a silencer muffler 29.

There are shown at 30 and 31 two small ducts which start from the duct 27, the former from a point upstream of the muffler 28, and the latter from a point downstream of the muffler 29.

The duct 31 opens into a chamber or space 37 whose constructional features are best seen in FIG. 2: the duct 30 is connected through the flange 32 to the counterflange 33 of a cylindrical section 34 which is jointed to a duct 35 opening into the induction duct 15.

From the cylindrical section 34 branches off a small tube 36 connected to the space 37.

In FIG. 2 there is shown in its constructional details the chamber 37 along with the cylindrical section 34 located between the ducts 30 and 35. There are indicated at 58 and 59 the arrows which show the direction of flow of the recycled gas. There is indicated at 38 a diaphragm having an opening 39 defining a choke or constriction whose value is fixed and which is inserted in the duct 30 by means of the flanges 32 and 33, and at 40 there is a butterfly valve pivoted at 41 to the walls of the section 34.

To the body of the valve 40 there is hingedly attached at 42 one end of a rod 43, the other end of the same rod being hinged at 44 to the central rigid portion 46 of a movable wall or diaphragm 45. The peripheral edge of the wall 45 is inserted between the flanges of two rigid half shells 47 and 48 of the chamber or space 37, which are kept assembled by a clamping ring 49. There are indicated at 50 and 51 the cavities confined by the movable wall 45 and by the walls of the half shell 48 and by the same movable wall 45 and the walls of the half shell 47, respectively.

The operation of the device described above is as follows: it is apparent that the diaphragm 45 is in equilibrium when the pressure obtaining in the duct 27, in the point where the duct 31 branches off, is equal to the pressure at the terminal point of the tube 30, where the duct 36 branches off, that is, between the fixed constriction 39 and the throttle 40: these two pressures are, in fact, those which act on the two faces of the diaphragm 45. Obviously, this condition of equality requires that the gas pressure drop in the portion of the duct 27 between the points where the ducts 30 and 31 branch off is maintained equal to the pressure drop undergone by the recycled gases by flowing through the tube 30 from the point where it branches off from the duct 27 to the zone immediately downstream of the choke or constriction 39.

At every variation of both the negative pressure in the manifold 15 and the pressure in the duct 27, the diaphragm 45 is shifted towards a new position of equilibrium corresponding to a different position of the throttle 40, so as to maintain a constancy of the ratio between the respective rates of flow of the exhaust and the recycled gases according to the objects of the invention.

According to a different embodiment, it is possible to measure the pressure drop the gases undergo when flowing through the portion of the exhaust duct 27 which extends from the point at which the recycling duct 30 branches off to the free discharge into the atmosphere.

In this case the device takes a particularly simple shape, as shown in FIG. 3: the face of the diaphragm which corresponds to the chamber 50, is in direct contact with the atmosphere, so that the duct 31 can be eliminated: the diaphragm 45 is in equilibrium when the pressure obtaining in the recycling duct, between the choke 39 and the throttle 40 is equal to the atmospherical pressure: that is to say that the pressure drop the gases undergo when flowing through the tube section located between the point of branching off of the duct 30 and its free opening into the atmosphere is equal to the pressure drop undergone by the recycled gases when flowing through the duct 30 from the starting point to a zone immediately downstream of the choke 39: also in this case such an equality ensures a constant ratio between the rates of flow of the exhaust gases and the recycled gases.

Numerous changes can be made in the embodiments shown herein: more particularly in FIGS. 1, 2 and 3, the pressure drop localized in the recycling pipe, determined by the choke 39, can be obtained in various ways or even avoided, by shaping the duct 30 in such a way that its resistance to the gas flow gives rise to a pressure drop of the desired value. Obviously, the obtention of the desired resistance with the use of a disc 38 having a calibrated opening permits an initial regulation of the ratio of the rates of flow which is very convenient and accurate.

When a variation is desired of the above cited ratio between the rates of flow, under particular operative conditions of the engine, it can be provided to place in the recycling duct an additional throttling member, as in FIG. 4, in which a throttle 55 is shown, which is freely pivoted to the wall of the tube 30 and can be controlled by the action of a rod 57 which acts on a lever 56 integral with the throttle.

The throttle 55 can be driven, more particularly, in the sense of being closed when the engine is required to deliver very small powers; in such a case, in fact, it is of minor importance to profit of the recycle of the exhaust gases: the mechanical linkage 57 can be connected to usual accelerator pedal 61, in the sense of closing the throttle when the pedal is released due to the bias of springs 62, or it can be controlled with a similar action by a device sensitive to the negative pressure in the intake duct of the engine, in the sense of being closed as the magnitude of the negative pressure is increased.

It is obvious that the throttle 55 when it is being closed, causes an increase of the resistance to the gas flow in the auxiliary pipe 30, thus causing the rate of flow of the recycled gas to diminish, with the result being a pressure drop in the pipe 30, which is equal to the pressure drop experienced in the exhaust duct 27. It is obvious that in such a way as the resistance in the pipe 30 is increased, the ratio between the gases recycled in the intake duct and the gases exhausted from the engine is decreased.

Claims

What is claimed is:

1. An internal combustion engine provided with an intake duct, an exhaust duct and an auxiliary piping connected to said exhaust duct to draw a portion of the gases flowing therethrough to discharge them into said intake duct, the improvement including first means sensitive to a pressure drop undergone by the gases which flow through at least a portion of the exhaust duct, second means operably related to the first means and sensitive to a predetermined pressure drop undergone by the gases when flowing through a portion of said auxiliary piping and a member for throttling in a variable manner said auxiliary piping, said member being driven by said first and said second means in the sense of keeping proportional the respectively sensed pressure drops.

2. The internal combustion engine according to claim 1, in which said first means are sensitive to the gas pressure in a point of the exhaust duct which is downstream of the connection of the auxiliary piping to said duct, and are sensitive, to the gas pressure at a point of said auxiliary piping which is upstream of said member, and drive said member to throttle said auxiliary piping so as to maintain the sensed pressure proportional to each other.

3. An internal combustion engine provided with an intake duct, an exhaust duct and an auxiliary piping connected to said exhaust duct to draw a portion of the gases flowing therethrough to discharge them into said intake duct, the improvement including first means sensitive to a pressure drop undergone by the gases which flow through at least a portion of the exhaust duct, second means operably related to the first means and sensitive to a predetermined pressure drop undergone by the gases when flowing through a portion of said auxiliary piping and a member for throttling in a variable manner the auxiliary piping, said member being driven by said first and said second means in the sense of keeping proportional the respectively sensed pressure drops, said first means being sensitive to the gas pressure in a point of the exhaust duct which is downstream of the connection of the auxiliary piping to said exhaust duct and sensitive to the gas pressure at a point of said auxiliary piping which is upstream of said member, and drive said member to throttle said auxiliary piping so as to maintain the sensed pressure proportional to each other, said first means consisting of a deformable diaphragm for separating two chambers, the first chamber being maintained in communication with a point of said exhaust duct which is downstream of the connection thereto of the auxiliary piping, the second chamber being maintained in communication with a point of said auxiliary piping, said diaphragm being operatively connected with said throttling member. in the sense of diminishing the flow cross-section of said auxiliary piping when the pressure in said first chamber is greater than the pressure in said second chamber and of increasing the flow-cross-section when the pressure of the second chamber exceeds that of the first chamber.

4. The internal combustion engine according to claim 1, characterized in that said exhaust duct opens into the atmosphere and said means are sensitive to the pressure at a point of said auxiliary piping and control said throttling means to maintain the sensed pressure in a constant proportion with respect to the atmospherical pressure.

5. An internal combustion engine provided with an intake duct, an exhaust duct, and an auxiliary piping connected to said exhaust duct to draw a portion of the gases flowing therethrough to discharge them into said intake duct, the improvement including first means sensitive to a pressure drop undergone by the gases which flow through at least a portion of the exhaust duct, second means operably related to the first means and sensitive to a predetermined pressure drop undergone by the gases when flowing through a portion of said auxiliary piping and a member for throttling in a variable manner said auxiliary piping, said member being driven by said first and second means in the sense of keeping proportional the respectively sensed pressure drops, said exhaust duct opening into the atmosphere and said means being sensitive to the pressure at a point of said auxiliary piping and controlling said throttling means to maintain the sensed pressure in a constant proportion with respect to the atmospherical pressure, said means comprising a chamber having a wall consisting of a deformable diaphragm and in communication with a point of said auxiliary piping upstream of said member, the latter being operatively connected to said diaphragm so as to diminish the cross-section of said piping when the pressure in said chamber is subatmospherical and increasing it when the pressure exceeds the atmospherical pressure.

6. The internal combustion engine according to claim 1, characterized in that in said auxiliary piping there is arranged a member for varying the resistance to gas flow in said piping.

7. An internal combustion engine according to claim 6, characterized in that said member is driven to vary said resistance by a sensing member of the power delivered by the engine in the sense of diminishing the resistance as the power is increased and vice versa.