EP0331574A1 - Device for preparing and distributing a carburetted mixture for a spark-ignited engine - Google Patents

Abstract

Device, particularly of the type comprising a main venturi tube (1) and a butterfly valve (8) controlled by a stepping motor, characterised in that it incorporates: - an auxiliary venturi tube (2) for the carburetted mixture feed, - an overflow tank (3), - a calibrated spray nozzle (4), - a cam (5) sealing all or part of the spray nozzle (4), - and a stepping motor (6) for controlling this cam (5). Application: In particular for the carburation of a controlled ignition engine. <IMAGE>

Description

The present invention relates to a device for preparing and distributing a fuel mixture intended for a spark-ignition engine.

Its purpose is to propose a system which makes it possible to control the fuel flow at constant air flow, so that the richness of the mixture becomes an active parameter of the operation of the engine and not a consequence of other adjustments.

It thus has as its object such a device of the type comprising in particular a main venturi tube and a butterfly controlled by a stepping motor which, according to an essential characteristic, incorporates:
- an auxiliary venturi tube for the fuel mixture supply,
- an overflow tank,
- a calibrated nozzle,
- a cam closing all or part of the nozzle,
- And a stepping motor for the control of this cam.

According to another particular feature, this overflow tank is connected to a fuel tank by a return pipe, and to the atmosphere by a vent pipe.

Fuel flow control is thus made possible at any engine operating point, which provides flexibility of using a single-point injector at a much lower cost.

All the additional circuits of the conventional carburetor are eliminated. The price of a stepper motor should not bring the cost of this system to a level higher than that of the conventional carburetor.

• - la figure 1 représente une vue schématique en coupe axiale d'un dispositif conforme à l'invention,
• - la figure 2 représente une vue schématique similaire pour une variante "double corps à ouverture simultanée",
• - la figure 3 représente une vue schématique illustrant le positionnement relatif des tubes à venturi de ce dispositif,
• - les figures 4A et 4B représentent un premier exemple de mon­tage d'une came et d'un gicleur constituant un sous-ensemble constitutif du dispositif de la figure 1,
• - la figure 5 représente un second exemple de montage de ce sous-ensemble,
• - et les figures 6A et 6B représentent un troisième exemple de montage de ce sous-ensemble.

Other particularities and advantages of the invention will emerge more clearly from the following description of two preferred embodiments, given by way of nonlimiting examples, with reference to the appended drawings in which:

• FIG. 1 represents a schematic view in axial section of a device according to the invention,
• FIG. 2 represents a similar schematic view for a “double body with simultaneous opening” variant,
• FIG. 3 represents a schematic view illustrating the relative positioning of the venturi tubes of this device,
• FIGS. 4A and 4B represent a first example of mounting a cam and a nozzle constituting a constituent sub-assembly of the device of FIG. 1,
• FIG. 5 represents a second example of mounting this sub-assembly,
• - And Figures 6A and 6B show a third example of mounting this sub-assembly.

In accordance with FIG. 1, the preferred device comprises in particular:
- a main venturi tube 1,
- an auxiliary venturi tube 2 conveying a fuel mixture,
- an overflow tank 3 connected to the reservoir by a return pipe 7 and to the atmosphere by a pipe 9 for venting to the open air,
- a calibrated nozzle 4,
a cam 5 closing all or part of the nozzle 4,
- a stepper motor 6,
- And a throttle valve 8 controlled by a stepping motor.

The venturi tube 1 is dimensioned so as to provide a maximum air flow demanded by the engine. It conveys clean air.

The venturi tube 2 supplies the carburetted air to the engine. Its arrangement with respect to the tube 1 is defined by the angles α, γ and the dimension x defined in FIGS. 1 and 3, the values of which are variable. Its size also varies depending on the engine.

The overflow tank 3 is supplied by a fuel pump. The return to the tank takes place via the pipe 7, the venting through the pipe 9.

The nozzle 4 has a section calculated so as to provide the maximum fuel flow admitted by the engine. The geometrical shape of its channel can be circular, elliptical, rectangular and it can penetrate or not inside the tube 2 (dimension y variable - figure 1).

The end of the nozzle on the tube side 2 can be bevelled or straight, and the projecting part in this tube can have a wall pierced radially with small diameter holes. The pipe channel of the nozzle may consist over all or part of its length of a fine lattice or of a set of capillaries.

The cam 5 which is activated in rotation by the stepping motor 6 closes all or part of the free section of the nozzle 4. Various mechanical systems, numerous respective arrangements of parts 4, 5 and 6 and multiple shapes relating to the surfaces in contact with parts 4 and 5 are possible.

Figures 4A and 4B, 5, 6A and 6B illustrate three examples of assembly of these parts.

In FIG. 5 is illustrated an "eccentric" arrangement where point A represents the center of rotation of a circular cam 5 (axis of the stepping motor 6), the arc B the location of the centers of this cam, the points m and n two distinct positions of the center of this cam for which the passage of the nozzle 4 is respectively closed and uncovered.

In FIGS. 6A and 6B, the passage section of the nozzle varies as a function of the angle of inclination ϑ.

The stepping motor 6 can be placed either inside the tank at a constant level 3, or outside the carburetor.

The throttle valve 8 controlled by a not shown stepping motor can be arranged upstream or downstream of the venturi neck 1.

At a given position of the butterfly valve 8 corresponds a flow rate Q1 and a pressure at the neck P neck 1 at the level of the venturi tube 1.

This pressure P col 1, lower than atmospheric pressure P atm, generates a flow rate Q3 and a pressure at the neck P col 2 in the venturi 2.

The metering of the admitted fuel no longer depends only on the level of the tank 3 and the section of the nozzle 4 delivering at the level of the neck 2.

Maintaining the unit richness in the event of a three-way catalysis or optimizing it in lean mixture type operation can thus be carried out (cf. single-point injection).

For operation at any speed and at any load under steady conditions, the displacement of the cam regulates the fuel flow. The emulsion tube of the conventional carburetor is eliminated.

In the case of a control loop, the constant level tank is not necessary.

For enrichment at idle, in recovery, at full load, choke, the appropriate positions of the cam adjust the fuel flow. The auxiliary circuits corresponding to these functions in the conventional carburetor are eliminated. In addition, the reduced fuel path between the tank and the venturi 2 reduces the inertial effects during acceleration.

A deceleration cut is possible by completely blocking the nozzle.

The throttle motor allows a stable position at idle and dispenses with the use of a damper during sudden decelerations.

The presence of the auxiliary venturi tube 2 makes it possible to increase the speed of passage of the air at the level of the nozzle and thus to improve the spraying. The various types of sprinklers listed above have the same properties.

The reduced length of the fuel line between tank and nozzle significantly improves the dynamics of the assembly.

Adequate sizing of the venturi tube 1 making it possible to obtain a sonic regime at the neck well after the appearance of this phenomenon at the level of the neck 2 allows a "double compound body" effect.

The use of an overflow tank makes the system almost insensitive to its inclination.

Possible extensions:

For certain uses, the overflow tank 3 can be replaced by a constant level tank.

The venturi tube 1 can optionally conduct a fuel mixture.

A “double body with simultaneous opening” system, an example of which is shown in diagram 2, is such that the fuel is supplied by a single auxiliary venturi. All the remarks concerning the basic system can be transposed there.

Claims (2)

1. Device for preparing and distributing a fuel mixture for a positive-ignition engine, of the type comprising in particular a main venturi tube (1) and a throttle valve (8) controlled by a stepping motor, characterized in that '' it incorporates:
- an auxiliary venturi tube (2) for supplying fuel mixture,
- an overflow tank (3),
- a calibrated nozzle (4),
- a cam (5) closing all or part of the nozzle (4),
- And a stepping motor (6) for controlling this cam (5). 2. Device according to claim 1, characterized in that the overflow tank (3) is connected to a fuel tank by a return pipe (7), and to the atmosphere by a vent pipe (9).

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