EP0589733B1 - Progressively shaped throttle valve body and manufacturing method thereof - Google Patents

Description

The present invention relates to a throttle body for a fuel injection device for an internal combustion engine, in particular for an injection device comprising electronic means for controlling the quantity of fuel introduced in each engine operating cycle.

The quantity of fuel injected per cycle must be proportional to the air flow admitted to the engine. In many injection devices currently used, this air flow is calculated by electronic means from signals indicating on the one hand the degree of opening of the butterfly valve (supplied for example by a potentiometer), on the other hand the pressure difference between the upstream and downstream of the butterfly, representative of the air speed. Satisfactory engine control at low loads (i.e. for small throttle openings) requires that the initial increase in flow be very gradual. In particular, driving pleasure is practically obtained, in the case of an electronically controlled injection device, only with an initial variation of the air flow as a function of the opening angle α of the butterfly having a shape of the genus shown schematically in thick lines in FIG. 1.

To obtain the required progressiveness, butterfly bodies of the type have already been proposed comprising a housing in which is formed an intake duct and a butterfly in the form of a circular or slightly elliptical disc, mounted on a median axis of rotation transverse to the duct. and movable between a minimum open position, possibly zero, and a maximum open position for which the butterfly is oriented parallel to the axis of the duct, the duct having a wall which has a complex shape, so that the passage section offered to the air increases at the start of the opening, as a function of the opening angle of the butterfly, much less rapidly than in the case of a cylindrical conduit.

In the case of a metal body, where the molding does not give a sufficient degree of finish, the complex shapes retained so far cannot be produced by simple machining and / or require rough drafts to be molded. In addition, many forms do not allow the butterfly to be mounted by simply inserting it along the axis of the duct, whereas this is an essential condition on an automatic assembly line.

However, there has been proposed (see FR-A-2663710) a butterfly body with a complex shaped duct which can be formed directly by molding, but only in the case of a constitution of synthetic material where the molding gives sufficient precision. However, the proposed form (in FR-A-2663710) based on an approach taking into account the passage sections rather than the flow rates, does not allow easy obtaining of all the laws of variation of the flow rate as a function of the opening , very different depending on the powered engine or the drive linkage, required by current manufacturers.

The invention aims in particular to provide a butterfly body that better meets those previously known to the requirements of practice, in particular in that it makes it possible to obtain all the required progressivity laws without however presenting difficulties in production or assembly. throttle or jamming (see EP-A-433518).

For this purpose, the invention provides a butterfly body of the type defined above, characterized in that the duct has a straight cylindrical section with a section corresponding to the shape of the butterfly in the latter's minimum open position, s' extending upstream and downstream of said minimum opening position, and present, in upstream and downstream of the cylindrical section and along the path followed by the upstream and downstream sections of the butterfly valve up to a determined opening angle of the latter, respective zones delimited by arcs of circles centered on the axis of the duct intake and decreasing radius from the cylindrical section.

As a general rule, the cylindrical section will be of circular section, which corresponds well to the usual forms of butterfly which are either with circular periphery, or with very slightly elliptical periphery when the position of minimum opening, possibly zero, of the butterfly is inclined by relative to a plane perpendicular to the axis of the duct.

In practice, the axial length of the cylindrical section will be chosen so that, at constant sonic pressure difference between upstream and downstream, the flow rate which passes when the section of the butterfly exceeds, upstream and downstream, the section cylindrical is between 160 and 180% of the flow corresponding to the minimum opening of the butterfly. This flow rate corresponding to the minimum opening can be that which passes through the clearance which remains between the edge of the butterfly and the intake duct, when the closing of the butterfly is limited by a stop so that the butterfly cannot come apply against the wall, or one that passes through a bypass duct providing in particular the flow of idle air.

The invention also provides a method for making a relatively simple metal butterfly body of the type defined above. The method comprises the steps of molding a blank having an internal passage having, upstream and downstream of a straight cylindrical section corresponding to a minimum opening position of the butterfly, respective zones, each zone having a section of revolution from that of the sides of the median plane towards which the edge does not move when opening from the minimum opening position and, having opposite side, an area the projection of which towards the axis of the duct increases from the plane containing the throttle axis to the orthogonal plane and containing the throttle axis, and for machining the above-defined zones in the form of arcs circles of decreasing radius from said cylindrical section to the extreme position taken by the butterfly for said determined maximum opening angle.

• la figure 1, déjà mentionnée, montre une loi souhaitable de variation du débit Q d'air en fonction du tirage d'un câble de commande du papillon ;
• la figure 2 montre un corps de papillon conforme à un mode particulier de réalisation, en coupe suivant un plan passant par l'axe du conduit d'admission et orthogonal à l'axe de papillon ;
• la figure 3 est une vue en coupe suivant la ligne III-III de la figure 2 ;
• la figure 4 est une vue de-dessus du corps de papillon de la figure 1, sur lequel la section droite aux niveaux Z0, Z1 et Z2 de la figure 2 a été indiquée en tirets ;
• la figure 5 montre une ébauche obtenue par moulage, utilisable pour constituer le boîtier d'un corps suivant la figure 2, la forme après usinage étant représentée en traits mixtes.

The invention will be better understood on reading the following description of a particular embodiment given by way of non-limiting example. The description refers to the accompanying drawings, in which:

• Figure 1, already mentioned, shows a desirable law of variation of the air flow rate Q as a function of the draw of a throttle control cable;
• Figure 2 shows a throttle body according to a particular embodiment, in section along a plane passing through the axis of the intake duct and orthogonal to the throttle axis;
• Figure 3 is a sectional view along line III-III of Figure 2;
• Figure 4 is a top view of the throttle body of Figure 1, in which the cross section at levels Z0, Z1 and Z2 of Figure 2 has been indicated in dashes;
• Figure 5 shows a blank obtained by molding, usable to form the housing of a body according to Figure 2, the shape after machining being shown in phantom.

The throttle body which will now be described is designed to obtain a law of variation of the flow rate of the kind shown in FIG. 1. The body shown in FIGS. 2 to 4 comprises a metal housing 10 made by molding and partial machining and a throttle 12 (FIG. 2) fixed in a shaft 14 allowing it to rotate about an axis orthogonal to the axis 16 of an intake duct 18 formed in the housing.

Conventionally, the butterfly valve 12 illustrated in FIG. 2 can be moved from the minimum opening position shown in solid lines to a full opening position where it is directed along the axis 16 of the duct 18. The minimum opening position can be fixed by the support of the edge of the butterfly, slightly elliptical in shape, against the wall of the duct, at a location where this wall is cylindrical, for an inclination relative to a plane transverse to the axis 16 of approximately 5 ° . The minimum opening position can also be fixed by an adjustment stop not shown. In this case, the minimum opening angle can be 0 ° or very close to 0 °.

In the embodiment shown in Figure 3, the shaft 14 rotates in bearings formed in bosses 20 of the body. One of its ends is fixed to the cursor of an angle sensor such as a potentiometer 22 indicating the angular position of the butterfly. The other end is fixed to a cam 24 to which the throttle control cable hangs. In the body can be formed a bypass passage 23 connecting the upstream of the butterfly an outlet 25 located downstream. On this passage is mounted a solenoid valve for opening it and therefore allowing an additional air flow to pass to that which bypasses the butterfly 12, at least when the latter is in its minimum open position.

The intake duct 18 can be viewed as comprising a straight cylindrical central section with circular section 26 and upstream parts (above the butterfly 12 in the case of an inverted butterfly body, where the air circulates in the direction indicated by arrow f) and downstream.

The central section 26 has a diameter such that the leaks along the edge of the butterfly 12, when the latter bears against the wall, are very reduced. The height h of this section is chosen so that the flow which passes around the butterfly as soon as the section exceeds, upstream and downstream, the cylindrical section is between 160 and 180% of the sonic flow corresponding to the opening minimum of the butterfly, while the possible bypass passage 22 is closed. In an advantageous embodiment because it makes it possible to minimize manufacturing tolerances, the section 26 will be symmetrical with respect to the axis of the butterfly shaft 14.

The upstream part of the intake duct 18 is asymmetrical with respect to a plane passing through the axis 16 and through the axis of the shaft 14. Half of the upstream part from which the edge of the butterfly moves apart during the opening (right half in Figure 2) is slightly conical or cylindrical and semi-circular section at each level along the axis 16. The other half, on the contrary, is present at each level z between the upper level z0 of the cylindrical section 26 and a level zm a section of composite shape. This section can be regarded as having a central part constituted by an arc of a circle centered on the axis 16 and of decreasing radius from the level z0 and side parts having a general shape of arc of an ellipse whose major axis is equal, at each level, to that of the section at the same level of the right half and whose minor axis increases from the central section. The minor axis of this ellipse is chosen so that the edge of the butterfly remains entirely along the zone where the cross section is in the form of an arc of a circle, until it reaches the level zm.

We see in Figure 2 that this leads to choosing the eccentricity of the ellipse at each level z0 to zm so that the intersections between the arcs of ellipse and the arcs of a circle are arranged along a line 30 starting from the tree and whose projection in the plane of Figure 2 is substantially straight.

We can also look at the perimeter of the central portion of the left part, at each level between z0 and zm, as the intersection of an elementary cylinder centered on the axis 16 and the plane connecting the axis of the tree from the butterfly to the extreme point of the evolutionary form thus formed, at the zm level.

Thanks to this arrangement, the butterfly can be mounted easily, even when it has a significant thickness. Indeed, along the plane passing through the axis 16 and the axis of the butterfly shaft 14, there is an insertion path where the transverse dimension of the duct is at least equal to the diameter of the butterfly.

When the thickness of the butterfly is not negligible, the shapes defined above can be slightly modified. In particular, line 30 then becomes the place of intersections between successive elementary cylinders and a plane passing through an axis offset from the axis of rotation, in the direction of the axis 16, the offset being substantially equal to half the thickness. of the butterfly.

The downstream part of the intake duct has the same constitution as the upstream part. It can be symmetrical with the upstream part. In the case illustrated in Figure 2 it is significantly shorter than the upstream part, for reasons of space of the body.

It can be seen in FIG. 2 that only the screened parts intervene to fix the law of variation of the flow rate as a function of the opening angle of the butterfly, until this angle reaches the value α. Consequently, it suffices to machine these parts of the conduit, the others possibly remaining rough. The machining is relatively simple, since it is limited to cutting along successive arcs of a circle, such as those indicated in z1 and z2 in FIG. 4 and which correspond to the levels z1 and z2 in FIG. 2.

It is possible to adopt symmetrical machined shapes upstream and downstream of the butterfly. However, it is often more advantageous to adopt separate shapes, which give more flexibility to adapt to the various laws required to vary the flow rate as a function of the opening angle.

The radii of successive circles, i.e. the evolution of the shape for successive opening angles can be developed in a manner known per se on a computer, using software transforming the data of a law of variation of the mass air flow rate as a function of the angle of the butterfly in an upstream form and a downstream form defined by separate coordinates. The software is designed so as to obtain continuity with the parts with a circular or elliptical cross section.

It is not necessary to describe here a software allowing to calculate the radius to be given to each level z1, z2, ..., zm because such software being within the reach of the skilled person. It is established taking into account the eccentricity chosen a priori for ellipses whose arcs are preserved on the machined case.

The housing is metallic (aluminum for example) and can be produced by pressure molding of a blank of the kind shown in FIG. 5, then machining on a machining center. The blank shown in Figure 5 is achievable without difficulty, with a core in two parts introduced on either side, along the axis. At each level along the axis, the left part above the central cylindrical section and the right part below this section present, at each level along the axis, a form of half-ellipse whose small axis is chosen so that the section just delivers passage to the butterfly when the latter opens. The extra thickness to be removed in the machined areas (represented by screened areas in Figure 2) is indicated in dashed lines in Figure 5. The software giving, with a step which can be very small (of the order of a tenth of a millimeter ) the radii of the arcs of successive circles from z0 to zm, the machining can be carried out in a very simple way, by modifying the machining radius each time the tool passes from one level to the next. Since the pitch is very small, a staircase surface is thus obtained which is comparable to a continuous surface. In the zone cylindrical central unit, the entire periphery is machined.

In practice, the opening angle α (Figure 2) for which the butterfly remains in a machined area will be between 35 and 50 °.

The butterfly can then be placed in a conventional manner. The butterfly shaft can be inserted, its slot being oriented in the direction corresponding to the complete opening of the butterfly. Then the butterfly 12 is slid along the axis. The shaft is rotated so as to bring the butterfly to the minimum open position. The fixing means such as screws, are put in place.

In the embodiment described so far, the butterfly has dimensions preventing it from arriving at an orientation where it is perpendicular to the axis 16: its position of abutment against the wall of the intake duct 18 makes an angle of a few degrees with the plane orthogonal to the axis 16. In this case, the section 26 may be limited to a circular line.

In yet another embodiment, the butterfly is arched, that is to say that its two wings form an obtuse angle with respect to each other. One of the wings is designed to bear against the wall of the intake duct at an angle of a few degrees with the plane orthogonal to the axis, while the other wing is then orthogonal to the axis. In this case, the section 26 is asymmetrical relative to the plane containing the axis of the butterfly shaft.

The invention would also be usable in the case of a butterfly which can rotate 180 ° around its axis, which is a solution sometimes adopted for butterfly bodies whose butterfly is not controlled directly by the driver, but by an engine taking into account various operating parameters and in particular the position of the accelerator pedal.

Plastic molding can be done with much more precision than that of metals, a body of the kind described above can advantageously be made of plastic by direct molding of a core. In this case it is the external shape of the core which is produced by machining to have the shape defined above.

Claims (6)

1. Butterfly valve assembly for a fuel injection apparatus of an internal combustion engine, comprising a body (10) formed with an admission passage (18) and a butterfly valve member having a circular or slightly elliptical disk shape, carried by a central rotation shaft (14) that extends transversally to the passage and is movable between a minimum opening position, possibly equal to zero, and a maximum opening position in which the butterly valve member lies substantially parallel to the axis (16) of the passage, the passage having a wall which has a complex shape for the cross sectional air flow area to increase at the beginning of the opening movement, responsive to the opening angle of the butterfly valve member, much less steeply than in a cylindrical passage,
      characterized in that the passage has a cylindrical length (26) whose cross-section corresponds to the shape of the butterfly valve member in the minimum opening position of the latter, extending upstream and downstream from said minimum opening position and has, upstream and downstream of the cylindrical length and along the path followed by the upstream and downstream edges of the butterfly valve member, up to a predetermined opening angle of the latter, respective zones which are defined by arcs of a circle centered on the axis of the admission passage and having radii which decrease starting from the cylindrical length.
2. Butterfly valve assembly according to claim 1, characterized in that the cylindrical length has a circular cross-section.
3. Butterfly valve assembly according to claim 1 or 2, characterized in that the cylindrical length (26) has an extent along the axis of the duct which is such that, for a same pressure differential between the upstream and the downstream sides of the valve member, the flow rate when the upstream and downstream edges of the valve member have just moved beyond said cylindrical length is between 160 and 180 % of the air flow rate corresponding to the minimum degree of opening of the valve member.
4. Butterfly valve assembly according to claim 1, 2 or 3, characterized in that the cylindrical length (26) is symetrical with respect to the axis of the butterfly valve member.
5. Butterfly valve assembly according to claim 1,2 or 3, characterized in that the cylindrical length is dissymetrical with respect to the axis of the valve member.
6. A method of manufacturing a body for a butterfly valve assembly according to any one of the preceding claims, characterized by the steps of: molding a blank having an inside passage presenting a generally cylindrical length, and respective zones upstream and downstream of the length, each zone having a cross-section of rotational symetry on that side of a mid-plane toward which the edge of the butterfly valve member does not move during opening from the minimum opening position and having, on the opposite side, a zone whose projection toward the axis of the passage increases from the plane containing the axis of the butterfly valve member and the axis of the admission passage to a plane which is orthogonal thereto and contains the axis of the butterfly valve member; and machining said zones as arcs of circles centered on the axis of the passage and having radii that decrease from said cylindrical length up to the limit position of the butterfly valve member for said predetermined maximum opening angle.

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