Fuel injection systems

Abstract

The device for the indirect injection of fuel into the intake tube upstream of the inlet valves comprises means for injecting at the intake time, into the combustion chamber, a metered amount of fuel directed to this end into a gaseous flow of air at substantially sonic speed, induced by a set of stepped tuyeres having a moderate divergent angle, at the level of the neck portion of said tuyeres. This device is applicable notably to the air-fuel feeding of engines for improving the fuel metering precision and the quality of the air-fuel mixture and therefore the degree of atmospheric pollution.

Description

This invention relates in general to fuel injection systems and has specific reference to improved methods and means for injecting fuel into internal combustion engines with a view to improving the spray conditions as well as the precision of the fuel metering action in the case of direct injection systems, i.e., when the fuel is injected directly into the intake manifold or induction pipe, upstream of the inlet valve.

The difficulties arising when attempting to obtain homogeneous air/fuel mixtures, i.e., mixtures wherein the fuel is perfectly atomized and distributed throughout the gaseous stream located between the point where the combustion mixture is formed and the inlet valves of an internal combustion engine are well known. This problem is particularly acute when the petrol pressure is relatively low, for the fuel output cannot be maintained at a sufficient value if the fuel is sprayed through the very small orifices necessary for producing an efficient atomization, as in the case of high-pressure injection systems. In a carburetor engine this atomization is improved by introducing additional air through an emulsion tube producing a preliminary air/fuel mixture before atomizing this emulsion more completely in a choke tube or a double (twin) diffuser disposed downstream of the emulsion tube.

In an indirect injection system as a rule only one injector is provided for either metering the fuel, in which case an electromagnetic injector of the type currently used in electronic injection systems may be used, or for atomizing the mixture; in this last instance gauged mechanical injectors are preferred, the metering function being devolved to a special pump or distributor. So far as the Applicant is aware, no injectors capable of performing both functions simultaneously have been proposed, this dual function being found only in the carburetor system.

It is the primary object of the present invention to similarly combine these two functions with a mixture homogeneousness greater than that provided by carburetors, and also with the metering precision peculiar to injection systems.

In the individual section of the intake pipe associated with each cylinder and located just upstream of the inlet valve, a stepped nozzle system is arranged for providing at the neck level of one of the nozzles a gaseous air flow at high and possibly sonic speed, into which a fluid fuel feed duct will inject a fuel dose at the level of said neck, said dose being controlled by means for injecting fuel under pressure upstream of said fluid fuel duct.

Throttle means are incorporated in the intake pipe for adjusting the mixture output downstream of said nozzles.

The aforesaid fuel injection means may be adjusted or set to produce a metered amount of fuel corresponding to heavy loads. In this case, a second metering device may be provided for operating the engine at low loads and idling speeds. This device according to a preferred form of embodiment of this invention, may consist of a second injector located downstream of the output throttling means, for example, beneath the butterfly valve. In a slightly more sophisticated and therefore more expensive version this device may consist of an injector delivering fuel into a second set of nozzles or tuyeres, like the main full-load injector.

It is another object of this invention to cause the fuel to be injected simultaneously at the level of various multiple stepped tuyeres, this arrangement permitting the reduction of outputs and obtaining a higher precision in the injection times and therefore a marked improvement in the definiteness and precision of the richness settings. As in the preceding case the fuel will be injected through injectors delivering the fuel into feed ducts leading to the neck portion of each tuyere.

The air output may be adjusted by using either a conventional butterfly valve or a guillotine or drop valve located upstream or downstream of the main atomizing device, or a tuyere located more downstream in the gas choke tube, this tuyere having a variable-section neck portion.

In a preferred form of embodiment of this invention, the use of two injectors incorporated in the intake manifold or pipe of an internal combustion engine will provide a sufficient degree of precision at all engine loads and speeds, notably in the case of electronic injection equipping a high-performance engine, while constituting a simple and economical system, as will appear in the following description given with reference to the accompanying drawings.

In a modified form of embodiment, the sonic diffusing tuyere of which the divergent cone has an angle equal to or less than 10.degree., is characterized in that its external envelope, along its divergent section and to a point located beyond the neck portion, comprises a cylindrical shoulder in which a circular fuel inlet channel or groove is formed, this shoulder being adapted to fit tightly in a diffuser support having a properly streamlined external contour, of same length as the fitting portion, said support merging at its end into the external cylindrical surface of the tuyere and being rigid with radial arms for connecting same to the inner wall of the diffuser supporting tube inserted in the flow passage. A radial feed passage communicating with the injector proper is formed through one of the arms of the diffuser support, at the same level as the circular feed channel into which said passage is caused to open. At least two radial, diametrally opposite orifices open into the circular channel formed in the neck portion of the tuyere. In order to deliver fuel simultaneously, these orifices are disposed symmetrically in relation to the axis of the main fuel feed passage from the injector.

With this simple construction the tuyere orifice is cleared completely at the level of its neck, so that only a very reduced dead volume is left for the fuel injection circuit, in the form of the radial passage and the circular channel downstream of the injector, thus improving the metering precision of the device.

In the drawings:

FIG. 1 illustrates in axial section an injection fuel feed system according to the method of this invention;

FIG. 2 is a modified form of embodiment of the arrangement shown in FIG. 1, and

FIG. 3 is a diagram plotting the torque and power output curves of an engine equipped with the device illustrated in FIG. 2.

Referring to the attached drawings and more particularly to FIG. 1, the intake device according to this invention comprises a main Venturi tuyere or nozzle 1, having a divergent section of moderate angular value in order to avoid the introduction of appreciable pressure losses which is disposed within an intake pipe 2; this divergent section may have for example an angle not in excess of 10.degree.. An auxiliary tuyere or nozzle 3 also referred to as a double diffuser, adapted to amplify the vacuum produced in the neck portion of the main Venturi 1, is provided just upstream of this Venturi, and has its outlet level with the neck of said main Venturi 1.

With this arrangement it is possible, without increasing the pressure losses due to moderate divergent angles, to cause a larger amount of gas to flow through a smaller cross-sectional area of the pipe. Thus, for instance, a 30-millimeter pipe arranged according to this invention will have the same output capacity as a 40-mm pipe, without throttling the engine.

A fuel injector 4 is adapted to inject the liquid fuel petrol into an injection passage 5 so that the fuel under pressure can be sprayed through the spout 6 of which the shape and number of spraying orifices are definitely immaterial; this spout 6 is located at the level of the neck of the auxiliary tuyere 3. With this arrangement the metered amount of petrol can be injected when the gas speed has its maximum value through the auxiliary tuyere neck. Considering the fact that the fuel thus injected is metered by the injector 4, the speed of this fresh gas flow may advantageously be equal to the speed of sound in order to ensure the best possible atomization, thus permitting the utilization of low-pressure injectors such as electromagnetic injectors as currently employed in electronic injection systems.

This device does definitely not interfere with the position of the butterfly valve 7 disposed downstream of the main tuyere 1 for controlling independently the adjustment of the intake mixture output. Considering the adaptation of this injection system, for example of an electronic character, to a high-efficiency engine, the chief difficulty to be overcome consists in obtaining a satisfactory fuel output at both idling speeds and maximum power-output speeds. At moderate loads a second injector 8 disposed downstream of butterfly valve 7 and delivering low fuel outputs will be used. In this case, this idling injector 8 will operate only at low loads, and injector 4 will operate alone only at high loads (corresponding for example to a butterfly valve position open at about three-fourths of its permissible movement). The adjustment precision is further improved by the fact it is independent for each cylinder.

The present invention is applicable more particularly to internal combustion engines equipped with indirect fuel injection systems or any other metering device capable of replacing the main injector 4, and also to high efficiency engines requiring more homogeneous air/fuel mixtures. Furthermore, this device will permit an easy adjustment of the tuning of the intake pipe of internal combustion engines due to the presence of the main tuyere 2, so that as a rule shorter intake pipes or tubes and more regular flow rates than with the use of purely cylindrical tubes can be contemplated. This fuel supply will also advantageously apply to continuous-combustion thermal engines such as steam engines, turbines, ramjets, pulso-jets, etc.

In the modified form of embodiment illustrated in FIGS. 2 and 3 it will be seen (FIG. 2) that a sonic tuyere or Venturi 1 is fitted in a supporting tube 2 mounted on the engine cylinder head 15. This tuyere 1 projects upstream beyond the flange of tube 2 for centering a flanged cylindrical body 9 having force fitted therein a diffusing tuyere support 10 in which a concentric streamlined socket 6 is mounted concentrically for supporting the auxiliary tuyere or Venturi 3, the socket 6 being connected to the tuyere 3 through a pair of opposite radial streamlined arms 7.

The auxiliary diffusing tuyere 3 is tightly fitted in the streamlined socket 6 so that its concentric external groove 14 constituting the feed channel be level with the radial feed passage 5 connecting said socket to the injector 4 mounted on said body 9.

Advantageously, the diameter of passage 5 will be of the order of 2 mm for an equivalent cross-sectional dimension of channel or groove 14.

Means for controlling the fluid output, for instance in the form of a butterfly shutter (not shown) are provided upstream of said body 9. An auxiliary injector for idling and moderate-load operation (not shown) may also be provided in the flanged tube 2.

At least two diametrally opposed radial holes 12 connect the circular channel or grooves 14 to the neck portion of diffuser tuyere or nozzle 3 in order properly to atomize the fuel in the center of the sonic stream. To obtain the simultaneous or synchronized operation of these holes 12, these are disposed symmetrically in relation to the axis of channel 5.

During the engine operation this stepped tuyeres arrangement while affording a high sonic speed in the central stream at the ingress of the combustion chamber permits an engine operation independent of the upstream tube tunings. The contour of the stepped tuyeres 1 and 3 reduces pressure losses to negligible values.

In the diagram of FIG. 3 the torque and power output values are plotted as a function of the engine speeds, on the one hand (dash-line curve) in the case of an engine equipped with conventional carburetor and on the other hand (dash and dot curves) in the case of an engine equipped with an injection device according to the present invention, the reference letter a denoting the torque and b the power output, and it will be seen that notwithstanding a reduction in the choke diameter (32 mm instead of 40 mm in the case of the carburetor engine) the engine performances are considerably improved and more particularly the torque curve is much better at low engine speeds and more regular at high engine speeds.

At these high engine speeds the mass output limited by the sonic character of the tuyere remains maximum and the speed remains constant. These results are obtained by virtue of the elongated shape of the tuyeres according to the proportions shown in the attached drawing (FIG. 2) wherein the diffuser tuyere 3 has a divergent cone long about ten times the throttling diameter of the neck where the injection is produced through the holes 12 in the case of tuyere 1, the length of the divergent cone being at least three times the diameter of the neck receiving the outlet end of the divergent of the diffuser tuyere 3.

Of course, this invention should not be construed as being strictly limited by the specific forms of embodiment shown and described herein, since various modifications and variations will readily occur to those conversant with the art without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims

What is claimed as new is:

1. A device for feeding internal combustion engines by indirect injection applied independently to each cylinder into an induction pipe upstream of an inlet valve, comprising:

a. a set of concentric stepped venturi means, disposed upstream of said inlet valve of each cylinder in an induction choke, for providing a substantially sonic gaseous flow of air; and

b. an adjustable injection means for delivering metered amounts of fuel into the neck portion of the central venturi means of said set of stepped venturi means, wherein an adjustable quantity of fuel is injected into the gaseous flow of air induced by said stepped venturi means and wherein said central venturi means includes an external cylinder having a shoulder in which a circular groove is formed; and said adjustable injection means includes a radial feed passage connected to said circular groove, said shoulder being fitted into a supporting socket, said central venturi means having at least two radial holes formed in diametrally opposite positions and symmetrically in relation to said radial feed passage for interconnecting said circular groove and said neck portion of said central venturi means and wherein the length of a divergent cone of said central venturi means is about ten times its inner diameter measured across its neck portion.

2. A device for feeding internal combustion engines by indirect injection applied independently to each cylinder into an induction pipe upstream of an inlet valve, comprising:

a. a first set of concentric stepped venturi means, disposed upstream of said inlet valve of each cylinder in an induction choke, for providing a substantially sonic gaseous flow of air;

b. a first adjustable injection means for delivering metered amounts of fuel at high engine speeds through an injection passage into the neck portion of the central venturi means of said first set of stepped venturi means, wherein an adjustable quantity of fuel is injected into the gaseous flow of air induced by said first set of stepped venturi means and wherein the length of a divergent cone of said central venturi means is at least three times the diameter of the neck portion of another venturi means of said set of stepped venturi means in which the outlet end of the divergent cone of said central venturi means is positioned; and

c. a second adjustable injection means for delivering fuel at idling and low engine speeds into said induction pipe downstream of said first set of concentric stepped venturi means.

3. A device for feeding internal combustion engines by indirect injection applied independently to each cylinder into an induction pipe upstream of an inlet valve, comprising;

a. a first set of concentric stepped venturi means, disposed upstream of said inlet valve of each cylinder in an induction choke, for providing a substantially sonic gaseous flow of air;

b. a first adjustable injection means for delivering metered amounts of fuel at high engine speeds through an injection passage into the neck portion of the central venturi means of said first set of stepped venturi means, wherein an adjustable quantity of fuel is injected into the gaseous flow of air induced by said first set of stepped venturi means and wherein said central venturi means includes an external cylinder having a shoulder in which a circular groove is formed, and said first adjustable injection means includes a radial feed passage connected to said circular groove, said shoulder being fitted into a supporting socket, said central venturi means having at least two radial holes formed in diametrally opposite positions and symmetrically, in relation to said radial feed passage for interconnecting said circular groove and said neck portion of said central venturi means; and

c. a second adjustable injection means for delivering fuel at idling and low engine speeds into said induction pipe downstream of said first set of concentric stepped venturi means.

4. A device according to claim 3 wherein the length of a divergent cone of said central venturi means is about 10 times its inner diameter measured across its neck portion.

5. A device according to claim 3 wherein an outer streamlined surface of said supporting socket merges along a line of continuity into an outer cylindrical surface of said central venturi means.