GB2526273A - Fuel injector - Google Patents

Abstract

A fuel injector nozzle assembly 12 has a hollow body 14 extending along a longitudinal axis A and containing a valve member 16 slidably guided by means of a first sliding guide G1 and a second sliding guide G2. The valve member 16 is displaceable between an open position where a valve seat 58 is distant from a seating surface 40 enabling fuel injection through spray holes 34 and, a closed position where the valve seat 58 is in contact with the seating surface 40 preventing fuel injection. The valve seat 58, the seating surface 40 and the spray holes 34 are arranged between upper guide G1 and lower guide G2. The invention addresses the issue of upward thrust variations on the valve seat 58 of the valve member 16, due to different areas being exposed depending on if the valve is seated or not. This variation in upward, or opening, forces makes it difficult to control the valve member movements.

Description

Fuel injector

TECHNICAL FIELD

This disclosure relates to the nozzle assembly of a friel injector used in a fuel injection equipment of an internal combustion engine.

BACKGROUND OF TI-IF INVENTION

In a high pressure fuel injector the injection events occur when a valve member slidably guided in a nozzle body, between an upper guide and a lower guide, lifts-up in an open position so a valve seat cooperating with a seating surface opens a passage for the fuel to flow toward a plurality of injection holes regularly arranged about the nozzle main axis. When the valve member goes down in a closed position, the valve seat comes in a sealing contact with the seating surface and closes said passage thus forbidding any fuel injection.

For efficiency purposes it is desirable that the fuel spray is well distributed through the injection holes.

Inside the body, the valve member is subject to opposed opening and closing forces generated by the fuel pressure acting on surfaces of said member.

The closing force, downwardly oriented, is due to the pressure acting on an upper thmst surface of the valve member, said surface being transversal to the main axis of the valve member while the opening force, upwardly oriented, is due to the pressure acting on a lower thrust surface that is a conical surface of revolution where the valve seat is. All forces applied on said conical surface add and resuft in the upward opening force. When the valve member is in open position the pressure applies on the all area of the conical surface while, when in closed position the pressure only applies on the limited portion that is upstream, or "above" as commonly said, of the valve seat. Therefore, as the area of the downstream thrust surface varies, the opening force varies and makes it difficult to control the valve member movements whether it is in an un-direct acting injector, where the opening and closing forces are un-equal and the valve member displaces under the influence of variations of hydraulic pressures or, it is in a direct acting injectors where the forces are substantially equal and cancel each other, the valve member being hydraulically balanced and directly piloted by an actuator.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to solve the above mentioned problem in providing a nozzle assembly of a fuel injector. The nozzle assembly has a hollow nozzle body extending along a longitudinal axis and inside ofwhich, a valve member is slidably guided by means ofa first sliding guide and a second sliding guide. The valve member is displaceable between an open position, where a valve seat is distant from a seating surface enabling fuel injection through spray holes and, a closed position where the valve seat is in complementary sealing contact with the seating surface preventing fuel injection.

The valve seat, the seating surface and the spray holes are arranged between the upper sliding guide and the lower sliding guide.

The hollow nozzle body is further provided with an upper female cylindrical guide face and, a lower coaxial female cylindrical guide face and, the valve member is provided with an upper male cylindrical guide face slidably engaged in the upper female guide face forming together the upper sliding guide and, a lower male cylindrical guide face slidably engaged in the lower female guide face forming together the lower sliding guide.

In one embodiment, the upper sliding has a larger diameter than the lower sliding guide and, in another embodiment; the upper sliding and the lower sliding guide have same diameters.

Furthermore, the lower female cylindrical surface axially extends through the wall of the nozzle body.

The valve member comprises a central shaft portion extending from the upper male cylindrical guide face to the lower male cylindrical guide face. A first thmst surface is defined at the upstream extremity of the upper male cylindrical guide face and a second thrust surface is conical and extends from the central shaft portion to the lower male cylindrical guide face.

The valve seat is arranged on said second thrust surface and the valve member is further provided with an annular groove circumventing the valve member and arranged between the second thrust surface and the lower male cylindrical guide face so that, the spray holes open into said annular groove.

In yet another embodiment, the lower extremity of the nozzle body is closed by a sealing mean that can either be integral with the nozzle body or that can be added such as a sealing plug arranged at the lowest extremity of the lower sliding guide. In this latter embodiment, the nozzle is further provided with a low pressure return conduit opening in the immediate vicinity of the sealing mean and extending toward a low pressure outlet so that, in use, fuel leaking through the lower sliding guide is able to evacuate via said return conduit.

The invention is also about a fuel injector provided with a nozzle assembly as set in any one of the preceding lines.

BRIEF DESCRIPTION OF TI-IF DRAWINGS

The present invention is now described by way of non-limiting example with reference to the accompanying figures where: Figure 1 is an axial section of a nozzle assembly as per the invention, Figure 2 is a detailed view of a valve member used in the nozzle of figure 1, Figure 3 is a detailed view of a nozzle body used in the nozzle of figure Figure 4 is an axial section of a nozzle assembly as per a second embodiment of the invention.

Figure 5 is an axial section of a nozzle assembly as per a third embodiment of the invention.

Figure 6 is a magnified view of a detailed of the lower part of the nozzle assembly.

Figure 7 is a magnified view of a magnified view of a detailed of the lower part of the nozzle assembly as per another embodiment of figure 6.

Figure 8 is an axial section of a nozzle assembly as per a fourth embodiment of the invention.

DESCRIPTTON OF THE PREFERRED EMBODIMENTS

To ease and clarify the following description a top-down orientation will be used in reference to the orientation of the figures. Words and expressions such as "top, upper, lower, over, above, under"... may be utilized without any intention to limit the scope of the invention.

A first embodiment of a fuel injector 10 is now described in reference to figure 1, 2 and 3, said injector 10 being provided with a valve member 16 hydraulically controlled, as it will be detailed below.

The fuel injector 10 extends along a longitudinal axis A, it has a nozzle assembly 12 comprising a hollow nozzle body 14 wherein is slidably arranged the valve member 16, also commonly identified as a needle shaft. Here, the nozzle body 14 is represented integral in one piece while alternatives are known where the body 14 is the assembly of two or more separate components fixedly arranged together.

The nozzle body 14 longitudinally extends from an upstream extremity face 18 transversal to the axis A, at the top of figure 1, to a downstream extremity disc-face 20, at the bottom of figure 1. The body 14 is holed from one extremity to the other and, the through hole 22 centrally opens in both upstream and downstream faces 18, 20. The through hole 22 comprises a plurality of consecutive coaxial sections that are, from top to bottom, an upper female cylindrical guide face 24 having an upper female diameter D24 then, a central bore 26 having a bore diameter D26, then a narrowing conical female face 28 and finally a lower female cylindrical guide face 30 having a smaller female diameter nfl I)., The central bore 26, with diameter D26, is here represented larger that the above upper female diameter D24 but, different design choices are possible where, the cylindrical surfaces 24, 26, have equal diameters or even where, the central bore 26 is narrower than the upper female cylindrical guide face 24.

It has been chosen to identify the diameters of female faces with a uppercase "D" and, diameters of male faces with lowercase "d", followed by the reference number of the cylindrical face.

In its upper end portion, the body 14 is further provided with a high pressure fuel inlet conduit 32 extending through the wall of the body from the upstream face 18 to the central bore 26.

In addition, the nozzle body 14 is provided in its lower end with a plurality of spray holes 34 regularly arranged about the longitudinal axis A, and extending through the wall of the body 14 from entries 36, opening in the upper part of the lower female cylindrical guide face 30, near the smallest section of the female conical face 28, to exits 38 opening on the outer surface of the wall body.

Just above the entries 36, is a valve seating surface 40 aimed at S cooperating with a valve seat 58 of the valve member 16. Said cooperation can be arranged, as magnified on figure 6, on the lower the edge of the female conical surface 28, or more upstream as magnified on figure 7, in an intermediate area of said female conical surface 28.

Multiple alternatives of spray hole geometries and arrangements are known but will not be discussed here any further as this disclosure provides a non-limiting example illustrating the invention that focuses on other aspects of the injector.

The valve member 16, now described, has an axially elongated central shaft portion 42, with central diameter d42 and, said shaft portion 42 is provided in its upper end portion 44 with an upper male cylindrical guide face 46, with upper male diameter d46. The upper guide face 46 extends up to an upper thrust surface 48 transversal to the axis A. The lower end portion 50 of the valve member 16 is provided with a male conical face 52 downwardly reducing in section and, below said conical face 52, extends a lower male cylindrical guide face 54, with lower male diameter d54.

Furthermore, the valve member 16 is provided with an annular groove 56 arranged in the joining area of the male conical face 52 and of the lower male cylindrical guide surface 54. As represented in the examples of figures 6 or 7, the groove 56 can be arranged so the cooperation of the valve seat 58 and seating surface 40 is on the edge -figure 6 -or in an intermediate position -figure 7 -of the conical surface.

The assembly and the operation of the nozzle assembly 12 are now described, The upper guide faces 24, 46, and the lower guide faces 30, 54, are complementary slidably engaged to respectively form upper Gi and lower G2 sliding guides for the valve member 16.

Minimal clearances El, E2, voluntarily exaggerated on the figures, are arranged between the cylindrical guide faces of the upper guide Ut and lower guide 02, in order to enable axial displacement of the valve member 16 relative to the nozzle body 14 but forbid any transversal motion.

Typical diameter values for the upper and lower guides GI, G2, are approximately 2mm, preferably 1.5 mm or even less. The axial length of the upper and lower guide 01, 02, can be of 2 mm or preferably 3 mm, or even longer. Diametral clearances El, E2, are about 5 rim (2,5 jim to the radius) while a preferred diametral clearance would be smaller such as 4 rim or event 3 rim.

Also, the upper and lower guides Gl, G2, should be as coaxial as possible.

The valve member 16 is able to axially translate between a closed position CP, where it is in its most downward position, the valve seat 58 being in sealing contact with the seating surface 40 and, a fully open position OP where the valve member is lifted upward, the valve seat 58 being distant with the seating surface 40.

As already mentioned, figures 6 and 7 detail alternative embodiments of the seating surface 40 and the valve seat 58, With reference to figure 6, when the valve member 16 is in closed position CP, the valve member 16 contacts the nozzle body i4 in the edge joining the female conical face 28 and the lower female cylindrical guide face 30 and, with reference to figure 7, the contact area is on the female conical face 28, in an intermediate position slightly above said edge.

As can be seen on both figures, the male 52 and female 28 conical faces have slightly different angles so, between them, a small conical space CS remains accessible to the fuel at high pressure which fills this space CS and generates on the male conical face 52 forces that result in a vertical opening force upwardly oriented, Also, as visible on the figures, the entries 36 of the spray holes face the annular groove 56 regardless of the valve member 16 open or closed position, As mentioned above, the first embodiment of figure t is for a hydraulically controlled valve member 16, Indeed, the valve member lôis subject to a downwardly oriented closing force generated by the fuel pressure in a control chamber 47 wherein protrudes the upper thrust surface 48 and, to the upwardly oriented opening force generated by the fuel pressure on the lower thrust surface The transversal area on which fuel generates the closing force is the entire area of the upper thrust face 48 while, for the opening force, the fuel generates forces on the male conical face 52 only between the upper edge of said conical face 52 and the valve seat 58. The equivalent transversal area of the lower thrust surface has a diameter d42-d54 smaller than the diameter of the upper thrust surface 48 and, anyway, no upward force applies on the central portion where the lower guide G2 is.

On the first embodiment of figure 1, the valve member 16 can be hydraulically actuated by varying the pressure in the control chamber 47. When said pressure is high, the upper thrust face 48 being wider, the valve member 16 is biased toward the closed position CP and, to the opposite, when said pressure in the control chamber 47 diminishes, the downward force diminishes as well and, the opening force becomes dominant biasing the valve needle 16 toward the open position OP.

A second embodiment of the invention is now described in reference to figure 4, the essential difference being that in this second embodiment the upper Gi and lower guides G2 have equal diameters.

The second embodiment provides a hydraulically balanced valve member 16 with equal and opposite opening and closing forces. Therefore this second embodiment is for a direct acting inj ector, where an actuator, non-represented, directly controls the valve member 16. Advantage of such hydraulically balanced needle is that the required actuator only needs to apply forces to displace the needle without having to counter hydraulic forces as in other known directly actuated needles. This would then require actuators that are able to generate high forces such as piezo-actuators. Furthermore, such a hydraulically balanced needle operates independently of the rail pressure and, the motion rate only depends on the actuator so, when fuel pressure is lowthe opening rates can remain fast, This is advantageous for emissions performance but also to make the injector control robust to pressure waves in the high pressure lines.

Indeed, the valve member 16 is subject to a downwardly oriented closing force generated by the fuel pressure on the upper thrust surface 48 which, in this second embodiment, is a transversal disc face 48 joining the upper guide male cylindrical face 46 and the central portion 42. In other words, the closing force is applied on a disc area that diameter is equal to the central portion diameter d42 minus the upper guide Gi diameter d46, At the lower end of the valve member 16, the configuration of figure 6 provides a lower thrust surface 52 that has a transversal area which diameter S equals the upper edge diameter d42 minus the lower guide diameter d54. Said area of the lower thrust surface 52 is consequently strictly equal to the area of the upper thrust surface 48 and, the valve member 16 is hydraulically balanced and it requires to be directly piloted by said non-represented actuator.

In the configuration of figure 7, the lower thrust surface 52 slightly increases between the closed arid the open position. In closed position CP the pressure in the conical space CS only applies on the male conical face 52 upstream the valve seat 58 while in open position OP, the pressure also applies on the minor area of the valve member 16 extending downstream the valve seat 58 until the diameter d54 of the lower male guide face 54, This slight variation in area causes a very minor variation of the opening force, variation which is much smaller than the variation induced in the prior art where there is no lower guide G2, and which does not prevent implementing said alternative in a direct acting in] ector, In a third embodiment represented on figure 5, the lower extremity of the lower female guide face 30 is sealed by a plug 60 or alternatively, the hole 22 previously introduced as a "through" hole 22 is there a "blind" hole 22, and is not opening at the downstream extremity 20 of the body 14.

The minor quantities of fuel that may still leak through the lower clearance E2 do not exit the injector 10 and enter at low pressure into the engine combustion chamber, Said fuel leaks are instead collected inside the injector body N, below the lower guide G2, and returned to a low pressure line via a return conduit 62 extending from an opening arranged in the immediate vicinity of the plug 60 to a low pressure outlet, On this third embodiment of figure 5, the low pressure return conduit 62 is arranged axially inside the valve member 16, Here again, and similarly as the second embodiment of figure 4, the needle is hydraulically balanced as the upper Gi and lower G2 guide diameters are equal and consequently, the hydraulic upward and downward forces are identical in strength and opposed in direction, Being hydraulically balanced, this injector of third embodiment is suitable for a direct actuation from an actuator, not represented. Mso because the region above the needle is used to collect the fuel leaking past the lower guide during injection, it must be kept at the low system return pressure. This is typically inferior to lObar and often close to lbar.

Consequently, this embodiment cannot be hydraulically actuated but must be directly actuated. Use of the direct actuator gives the nozzle the benefits as for the second embodiment.

A fourth embodiment, a hydraulically controlled alternative to the third embodiment of figure 5, is now described in reference to figure 8. To enable the hydraulically control, a variable unbalanced force needs to be applied on the needle, Therefore, in its upper portion, the nozzle assembly 12 is provided with a first upper guide 011 that is the upmost guide as shown on the figure, and a second upper guide 012 that is just below. The first upper guide 011 has a smaller diameter than the second upper guide and, in between said two guides, is arranged the control chamber 47 wherein fuel flows via a specific inlet conduit, not represented. Control of the pressure via a well-known control valve enables to vary the pressure in said chamber 47 and to allow motion of the valve member 16.

In the description the references hereafter listed have been utilized, fuel injector 12 nozzle assembly 14 nozzle body 16 valve member 18 upstream extremity transversal face of the body downstream extremity disc-face of the body 22 through longitudinal hole 24 upper female cylindrical guide face 26 central bore 28 female conical face lower female cylindrical guide face 32 high pressure fuel inlet conduit 34 spray holes 36 entries of the spray hole 38 exits of the spray holes valve seating surface 42 central portion of the valve member 44 upper end portion of the valve member 46 upper male cylindrical guide face 47 control chamber 48 upper thrnst transversal surface lower end portion of the valve member 52 male conical face -lower thrust surface 54 lower male cylindrical guide face 56 annular groove 58 valve seat plug 62 low pressure return conduit Method of manufacturing the nozzle body providing a blank drilling step boring step surfacing step -honing Method of manufacturing the valve member 210 providing a blank 220 turning 230 grinding 240 surfacing D24 upper female diameter D26 bore diameter of the nozzle body D30 lower female diameter d42 central diameter of the valve member d46 upper male diameter d54 lower male diameter A longitudinal axis CP closed position OP open position El upper diametral clearance (D24 -d44) E2 lower diametral clearance (D30 -d54) Ut upper sliding guide 02 lower sliding guide first upper guide G12 second guide CS conical space

Claims (3)

1. CLAIMSNozzle assembly ( 2) of a fuel injector (10) having a hollow nozzle body (14) extending along a longitudinal axis (A) and inside of which, a valve member (16) is slidably guided by means of a first sliding guide (GI) and a second sliding guide (G2), the valve member (16) being displaceable between an open position (OP) where a valve seat (58) is distant from a seating surface (40) enabling fuel injection through spray holes (34) and, a closed position (CP) where the valve seat (58) is in complementary sealing contact with the seating surface (40) preventing fuel in] ection, characterized in that the valve seat (58), the seating surface (40) and the spray holes (34) are arranged between the upper sliding guide (01) and the lower sliding guide (02).
2. 2. Nozzle assembly (12) as set in the preceding claim wherein the hollow nozzle body (N) is provided with an upper female cylindrical guide face (24) and, a lower coaxial female cylindrical guide face (30) and wherein, the valve member (16) is provided with an upper male cylindrical guide face (46) slidably engaged in the upper female guide face (24) forming together the upper sliding guide (GI) and, a lower male cylindrical guide face (54) slidably engaged in the lower female guide face (30) forming together the lower sliding guide (G2).
3. 3. Nozzle assembly (12) as set in any one of the preceding claims wherein the upper sliding (01) has a larger diameter (D24, d46) than the lower sliding guide (02) (D30, d54), 4, Nozzle assembly (12) as set in any one of the claims 1 or 2 wherein the upper sliding (01) and the lower sliding guide (02) have same diameters.5. Nozzle assembly (12) as set in any one of the claims 2 to 4 wherein the lower female cylindrical surface (30) axially extends through the wall of the nozzle body (14).6. Nozzle assembly (12) as set as in any one of the claims 2 or 5 wherein the valve member (16) comprises a central shaft portion (42) extending from the upper male cylindrical guide face (46) to the lower male cylindrical guide face (54).7, Nozzle assembly (12) as set in claim 6 wherein a first thrust surface (48) is defined at the upstream extremity of the upper male cylindrical guide face (46) and wherein a second thrust surface (52) is conical and extends from the central shaft portion (42) to the lower male cylindrical guide face (54).8. Nozzle assembly (U) as set in claim 7 wherein the valve seat (58) is arranged on said second thrust surface (52) and wherein the valve member (16) is further provided with an annular groove (56) circumventing the valve member (16) and arranged between the second thrust surface (52) and the lower male cylindrical guide face (54) so that, the spray holes (34) open into said annular groove (56).9, Nozzle assembly (12) as set in any of the claims ito 4 wherein the nozzle body (14) is provided with a sealing mean (60) either integral to the nozzle body (14) or added such as a sealing plug (60) arranged at the lowest extremity of the lower sliding guide (G2).10. Nozzle assembly (12) as set in claim 9 further provided with a low pressure return conduit (62) opening in the immediate vicinity of the sealing mean (60) and extending toward a low pressure outlet so that, in use, fuel leaking through the lower sliding guide (G2) is able to evacuate via said return conduit (62).11. Fuel injector (10) provided with a nozzle assembly (12) as set in any one ofthe preceding claim,