GB2311558A

GB2311558A - Fuel injection nozzle with compressive radial pre-loading

Info

Publication number: GB2311558A
Application number: GB9705303A
Authority: GB
Inventors: Smith R Dhun; Richard Rustic; Robert W Martin Jr
Original assignee: Stanadyne Automotive Corp
Current assignee: Stanadyne Automotive Corp
Priority date: 1996-03-28
Filing date: 1997-03-14
Publication date: 1997-10-01
Also published as: GB9705303D0; BR9701577A; FR2746856A1; JPH1030529A

Description

FUEL INJECTION NOZZLE WITn COMPRESSIVE RADIAL PREwLOADING anrlrlurml 0 e Invention The present invention relates to a fuel injection nozzle to be secured to the cylinder head of an internal combustion engine.

U.S. Patent No. 4,205,789 issued June 3, 1984 for "Fuel Injection Nozzle and Clamp Assembly", describes the operation of a fuel injection nozzle of the inwardly opening1 pressure-operated type. Conventionally, such nozzle assemblies include a nozzle having a valve chamber with a valve seat and a discharge tip at one end thereof, a pressure operated valve slidably disposed in the valve chamber for controlling fuel flow through the discharge tip, and a fuel inlet member providing a fuel inlet passage connecting with the valve chamber. Fuel is conventionally delivered at a pressure of about 12,000 psi, against the bias of a spring, resulting in a rapid succession of high pressure pulses within the valve chamber and fuel delivery passage.

Various modifications and improvements have been made over the years, with a more recent objective of attaining injection at higher pressures than were previously utilized. Certain aspects of the nozzle body pose problems in achieving higher pressure operation. The valve chamber and fuel delivery passage typically intersect at an enlarged portion, or sump, of the valve chamber. Given that the diameter of a typical nozzle body is only about 1.5 cm or less, and that the sump plus the fuel passage to the sump must occupy a significant portion of the cross-section in a particular plane of the nozzle body, it is understandable that certain structural features or formations in the vicinity of the sump, will experience high stresses during each fuel injection pulse. Moreover, a very high peak to average stress factor, arises in the thin volume, or web, of material between the valve chamber and the fuel passage, in the vicinity of the intersection of the fuel passage with the sump. Evidence of stress-related cracking has been observed. In particular, a duck bill nozzle body fracture originating at the fuel inlet and sump intersection was observed during laboratory testing of an injector operated at about 17,000 psi peak injection.

Susceptibility to such stress related failure poses a significant obstacle to eventual realization of fuel injectors operating at increased pressure ratings, i.e., 20,000 psi and above. This problem is particularly troublesome, because of the desirability of operation at higher pressure, without altering the dimensional envelope of nozzles and nozzle assemblies which are in current use. Moreover, the higheststrength steels available for fabrication as fuel injector nozzles, are already in use, so that higher pressure capability cannot be achieved by merely upgrading the choice of materials.

Accordingly, a need has arisen for increasing the pressure handling capability of fuel injection nozzles, without changing the dimensional envelope, material selection, and installation compatibility of currently available fuel injector nozzles.

Summary of the Invention This problem is solved in accordance with the present invention, by providing means for maintaining a compression pre-stress on the nozzle body, acting radially inward toward the intemal region of the nozzle body, where high peak stresses arise during the fuel injection pulsing.

In nozzle assemblies of the type where a nozzle retaining nut secures the nozzle body to a nozzle holder, this compression pre-stress is preferably generated by providing a tapered portion on the nozzle retaining nut, acting against a mating tapered surface on the nozzle body, such that as the nut is torqued to draw the nozzle body toward the nozzle holder, the tapered surfaces are compressed against each other, thereby giving rise to a radially inward force component.

Altematively, a tapered washer may be interposed between a conventional retaining nut and a tapered surface of the nozzle body, for achieving the same compression pre-stress in the nozzle body. In this general aspect of the invention, a radially inward compressive pre-stress may be achieved anywhere in a nozzle body having at least one bore penetrating the upper end of the body and extending in a generally longitudinal direction into the interior or the body. A retainer nut draws the nozzle body toward the nozzle holder axially, with the improvement that the retaining nut includes means for generating a radially inward force component to compressively pre-stress the interior of the body around the bore, as the retaining nut draws the nozzle body axially toward the nozzle holder.

In a third alternative, a reinforcing ring may be pre-shrunk against the nozzle body substantially laterally of the region of peak intemal stress, for maintaining the desired compression pre-stress.

It should be appreciated that, with the preferred embodiment, only minimal changes are required to be made on a conventional nozzle, for significantly increasing the pressure handling capability. For example, computerized modelling of stress distribution in a one type of conventional nozzle body predicted a maximum Von Mises stress of 112,724 psi, and a Hoop stress of 95,788 psi, at an intemal pressure of 20,300 psi. This nozzle body was under an axial load due to the retaining nut torque, equal to 4,200 Ibs. By providing a 30 external taper on the nozzle body, laterally of the sump, and a corresponding 30 intemal taper on the retaining nut, with all other conditions identical, the resulting maximum Von Mises stress was 92,280 psi with a Hoop stress of 83,884 psi. The addition of the 30 body-to-nut contact angle imparted a radial force component to the body, which resisted expansion of the valve chamber during pulsing, resulting in lower stress levels. It is believed that the present invention can readily achieve a pre-stress of up to about one half the expansion stress experienced by the valve chamber, at 20,000 psi.

This example is noteworthy, because the retaining nut, which is normally used to provide only an axial load on the nozzle body, was easily modified to provide an effective radial pre-load component, without changing the dimensional envelope of the nozzle. In particular, not only did the modified nut have the same length and outer diameter as the original nut, but this dimensional consistency in the nut has the further advantage that the tip portion of the nozzle body, need not be lengthened to accommodate the increased pressure capability.

In many implementations of the improved nozzle, the lower end of the retaining nut engages a mating surface on the socket in the engine cylinder head. In yet a further advantage of the present invention, the axial clamping force in the socket is transmitted to the mating tapered surfaces, and thereby enhances the radial pre-load forces, over and above that provided by the retaining nut itself.

Therefore, the advantage achieved in normal operation, is even more favorable than that indicated by the computer modelling, which did not account for the enhancement due to mounting of the nozzle in the engine.

The invention does not, however, rely on the enhancement effect resulting from mounting in the engine. In some nozzle designs, the compressive force may be achieved by means other than the retaining nut. In yet other nozzle designs, the region of highest internal stresses (e.g., at the intersection of the fuel passage and valve chamber, particularly the sump), may not be located within the envelope defined by the installed retainer nut. In these circumstances, a heat-shrunk ring can be utilized to provide the compressive pre-load laterally of the sump region.

The internal taper on the ring or retaining nut can easily be optimized for a given nozzle design, but would typically fall within the range of about 10 -60 , preferably 30"-45". In some situations, it may be desirable to provide a very steep taper angle, with the tapered surfaces extending over most or all of the axial extent of the nozzle body (particularly the valve guide portion of the nozzle body). In general, where the internal features of the valve body generate high peak to average internal stresses, improved pressure handling capability would require that the compressive pre-stress be focused on the region of peak stress. On the other hand, where the nozzle internal features generate a relatively lower peak to average stress factor, the overall pressure handling capability may be maximized by distributing the compressive pre-stress over a greater axial extent of the nozzle body.

The optimum taper angle also depends on the axial load required to seal the nozzle body to the nozzle holder, and to seal the nozzle assembly in the socket of the cylinder head. Computer analyses of conventional retainer nuts or conventional bodies under typical clamping axial forces of 3,000-6,000 Ibs, indicate a high margin to failure.

Therefore, retainer nuts modified according to the present invention can be subjected to higher than conventional loading, to generate an effective radial pre-stress component, while maintaining conventional axial clamping forces necessary for satisfying the sealing requirements.

Brief Deoersption f (he Drawings These and other objects and advantages of the invention will be evident from the description which follows and accompanying drawings, in which: FIG.1 is a cross-sectional view of a fuel injection nozzle and holder assembly according to one embodiment of the present invention; FIG.2 is a fragmentary top view of the nozzle and holder assembly of FIG.1, illustrating a clamp member used to secure the nozzle to a cylinder head; FIG.3 is an end view of the nozzle and holder assembly of FIG.1; FIG.4 is an enlarged, cross-sectional view, of a variation of the embodiment shown in FIG.1; FIG.5 is a cross-section view, taken along line 5-5 of FIG.4; FIG.6 is a section view similar to FIG.4, of a second embodiment of the invention; FIG.7 is a section view similar to FIG.4, of a third embodiment of the invention; and FIG.8 is a section view similar to FIG.4, showing a fourth embodiment of the invention.

Deecriptin elE tle Preferred Eml~imenf FIG.1 shows a fuel injection nozzle and holder assembly having a nozzle, indicated generally at 10, comprising a tubular noz=le body 12 and a tubular nozzle holder 14. Nozzle body 12 is a single-piece component which provides a discharge tip 16 at its front end and a valve guide 18 at its back end. The nozzle body includes a bore 20 along axis 21 which provides a valve chamber in the nozzle body.

Discharge tip 16 includes a conical valve seat 22 and at least one discharge orifice 24 through which fuel is discharged. A retaining member or nut 26 is adapted, via intemally threaded trailing portion 27, to hold the back end 29 of nozzle body 12 against the forward end 31 of nozzle holder 14, as the threads 27 are advanced against external threads 33 on the nozzle holder 14. A guide pin 28 on the holder 14 is received in a suitable hole 35 formed in the end of nozzle body 12 to ensure proper alignment. The contact between surfaces 29 and 31 is maintained as a result of the contact between internally tapered surface 37 on retaining nut 26, and the externally tapered mating surface 39 on the valve guide 18 of the nozzle body 12.

For reasons to be explained more fully below, the mating tapered surfaces implement the key functional advantage of the present invention, namely, providing a compressive force, acting toward the central axis 21, for restraining the expansion of the chamber 20 and passage 34 within the nozzle body, thereby avoiding stress related failures.

Tubular nozzle holder 14 includes a longitudinal bore 30 in coaxial alignment with central bore 20 of the nozzle body. An enlarged cross bore 32 formed in nozzle holder 14 intersects its longitudinal bore 30 adjacent to the outer end of the nozzle holder. In addition, nozzle body 12 and nozzle holder 14 include aligned fuel feed passages 34 and 36 respectively, which provide communication between cross bore 32 and the valve chamber. A rod-like plunger or valve, generally 40, includes a rear, cylindrical bearing portion 42, slidably mounted in central bore 20 of valve guide 18 and a front-reduced diameter stem portion 44 having a conical tip 46 which cooperatively engages valve seat 22 to control the discharge of fuel from the valve chamber through the discharge orifices 24. A projection 48 extends from the rear end of valve 40 into longitudinal bore 30 of nozzle holder 14. A coil spring 50 located within longitudinal bore 30 engages a spring seat 52 which, in tum, engages extension 48 to normally bias conical tip 46 of valve 40 into engagement with valve seat 22. A small clearance 54 is provided between valve 40 and nozzle holder 14 to limit the lift of the valve.

A cylindrical fuel inlet member, generally 56, extends through cross bore 32 in nozzle holder 14 and includes a stud portion 58 and an inlet portion 60 projecting outwardly from opposite sides of the nozzle holder. Preferably, inlet member 56 may be copper brazed to nozzle holder 14. Inlet portion 60 includes an axial fuel inlet passage 62 and a radial port 64 to provide communication between the fuel inlet passage and fuel feed passages 34 and 36. Inlet member 56 also includes a cross bore 66 aligned with longitudinal bore 30 in nozzle holder 14. An adjustment screw 68 is threadably mounted within longitudinal bore 30 adjacent to the outer end of nozzle holder 14 and extends through cross bore 66 in inlet member 56 into engagement with coil spring 50. The screw is adjustable via a hex socket 70 formed at its outer end to adjust the compression of coil spring 50. A lock nut 72 is threadably mounted on the outer end of adjustment screw 68 and engageable with the outer end of nozzle holder 14 via a washer 74 to lock the screw in place. A central bore 76 in screw 68 provides a leakage passage for any fuel which enters the spring chamber.

The fuel injection nozzle and holder assembly includes clamp means straddling the nozzle holder body and engaging the inlet member on opposite sides for securing the assembly to the cylinder head. In the illustrated arrangement, an elongated clamp member, generally 80, comprises a flat piece of sheet metal formed into a Ushaped channel having an elongated flat base 82 and a pair of upstanding flanges 84 and 86 extending along opposite longitudinal edges of the flat base. The ends of base 82 are turned in the opposite direction from side flanges 84 and 86 to reinforce the base in a lateral direction. A central opening 88 is provided in flat base 82 for receiving tubular nozzle holder 14. Flange 84 includes a concave recess, e.g., a rounded notch 90 (FlGs.1 and 2), which intersects central opening 88 and engages stud portion 58 of inlet member 56. A similar concave recess or notch 92 (FIG.1) is provided in flange 86 for engaging inlet portion 60 of the inlet member. A pair of bolts 94 project through holes 96 located adjacent to the opposite ends of flat base 82 of clamp member 80 and are provided with a pair of nuts 98 to hold down the clamp member and secure the nozzle to the cylinder head 95.

It can thus be understood that a clamping force is generated between the nozzle holder 14 and the valve body 12, as a result of the torquing of the retaining nut 26 along engaged thread portions 27,33.

In conventional practice, where the mating surfaces 37,39 are flat (horizontal), a clamping load in the range of 3,000-6,000 Ibs is achieved. In addition, the other clamping means associated with clamp member 80, urges the substantially flat front surface 41 of the head 43 of retaining nut 26, against a corresponding socket surface in the cylinder head, with a force typically in the range of 2,000-5,000 Ibs. It can be appreciated that the axial force associated with clamp 80, is transmitted through the mating surfaces 37,39, thereby enhancing the radially inwardly directed force component associated with the tapered surfaces.

FIGS. 4 and 5 illustrate a variation 100 of the invention, in which structure corresponding to functionally similar structure in FIG.1, is designated by a numeric identifier that is increased by 100. Of particular significance in both variations, is the cooperation between the nozzle body 12,112 and the associated retaining nut 26,126 as the threaded portion 27,127 of the nut is advanced. The tapered surfaces 37,39 and 137,139 maintain a compression pre-stress on the nozzle body, having a vector component acting radially inward toward the intersection of the fuel passage 34,134 with the valve chamber 20,120.

The tapered surfaces transmit a longitudinal clamping force component parallel to the axis, for drawing the body and holder (not shown) together, and an inward force component directed radially inward toward the axis, for generating the desired compressive pre-stress. Preferably, the tapered surface 39,139 of the nozzle body is situated laterally of the sump portion 20b,120b, which in a conventional manner, is an enlarged sub-region in the valve body, between substantially cylindrical portions 20a,120a, and 20c,120c. In the illustrated embodiments of FlGs.1 and 4, the sump is situated within the valve guide portion 18,118, of the valve body 12,112.

The fuel passage 34,134 typically penetrates the surface 29.129 at the upper end of the nozzle body 12,112, and extends in a generally longitudinal direction into the interior of the body, obliquely toward the axis 21,121, such that the passage intersects the sump 20b,120b, very near to where the upper valve chamber portion 20a,120a, begins to enlarge to form sump 20b,120b. As a result, a relatively thin web 12a,1 12a of material is situated at the intersection of the chamber 20,120, and the fuel passage 34,134. Analyses and laboratory results have shown that this web experiences the highest peak to average stress within the valve body 12,112 and will experience stress-related failure if fuel is delivered through passage 34,134, at higher than conventional pressures, especially if pressures in excess of 20,000 psi are desired.

In accordance with the embodiment of the invention illustrated in FlGs.1 and 4, the taper angle at the mating surfaces between the valve guide 18,118 and the retaining nut 26,126, is ideally in the range of 30 -45 , taken with respect to a reference plane p which is perpendicular to the nozzle axis. A common feature of the embodiments shown in FlGs.1 and 4, is that the lower end 41,141 of the retaining nut, is adapted to bear against the socket of the cylinder block, such that the force acting between the tapered surfaces 37,137 and 39,139 due to the torquing of the retaining nut, can be enhanced by the axial loading of surfaces 41,141 against the cylinder head. One can appreciate, however, by close comparison of the embodiments of FIGs.

1 and 4, that it is immaterial to the invention, how far the shoulder head portion 43,143 of the retainer nut 26,126 extends below the sump 20b,120b or along the discharge tip portion 16,116 of the nozzle body 12,112. Moreover, it is also immaterial to the invention, that the outer surface of the head portion 43,143, may have a different profile as between the embodiments shown in FIGs. 1 and 4.

FIG.6 shows a second embodiment, which illustrates the invention in a more generic context, in which fuel passage 234 intersects valve chamber 220 to form an internal region 21 2a of peak to average stress. The tapered exterior surface 239 on the nozzle body mates with the intemally tapered surface 237 on retaining nut 226, at an angle of 60". The tapered surfaces are situated substantially laterally of the intersection of passage 234 with chamber 220. In general, the tapered angles can fall in the range of 10 -60 , but as noted above, 30"-45" is preferred.

Inspection of FIG.6 will reveal that in this embodiment, the head portion 243 of the retaining nut 226 has a lower surface 241 which is at an elevation above shoulder 218a on valve guide 218. In this embodiment, the surface 21 8a would clamp against the cylinder head, rather than surface 241 on the retaining nut 226. Although in this embodiment the full advantage of the invention is not achieved, because the clamping force to the cylinder head does not enhance the clamping force generated by the nut 226, the invention nevertheless provides significant compression pre-stress relative to conventional practice, where no radial pre-stress is provided anywhere.

FIG.7 illustrates a third embodiment 300, in which the exterior tapered surface 339 on the valve body 312 is substantially identical to that on the valve body 112 of FIG.4, but the surface acting against the body taper, Is formed by a ring 337 having a tapered interior shoulder 337' and a square outer comer which Is supported by a flat counter comer of the head 343 on the retaining nut 326.

FIG.8 shows another embodiment 400, which is particularly applicable in a nozzle wherein the sump 420b in the valve chamber 420 is situated at an elevation in the nozzle body 412, which is below the elevation 1e1 where the retaining nut would engage the body 412. In this arrangement, an exterior taped or cylindrical surface 439 is formed in the valve body laterally of the sump, but the corresponding intemally tapered or cylindrical surface 43T is provided by a ring 437 which is heat-shrunk against the surface 439 of the body.

Practitioners in this field of technology, can readily appreciate that the invention as described herein, may be implemented in other embodiments of a fuel injection nozzle and associated holder and clamping assembly. In particular, the nozzle body might include a discharge tip portion which has a greater axial length than the valve guide portion, or as suggested in the embodiment of FIG.8, the discharge tip portion may consist only of a valve seat formed in the lower end of the valve guide. Similarly, the geometric relationship between the retaining nut, valve guide, and discharge tip, may vary considerably from that illustrated herein. Furthermore, the location of the highest peak to average stress within the nozzle body, may not necessarily depend on the presence of a sump within the body, although it is expected that regions of high intemal stress would occur in the vicinity of the wall surface of at least one bore penetrating the upper end of the valve body and extending in a generally longitudinal direction into the interior of the body. This bore can be oriented axially through the nozzle, such as the valve chamber, and/or obliquely to the axis, such as the illustrated fuel passage. The particular angle of the tapered surfaces which generate the compression pre-stress, can vary according to whether a relatively high pre-stress is desired on a relatively localized region within the valve body, or whether a relatively lower pre-stress is desired over a relatively greater axial extent of the body. These and similar optimization options can, based on the description herein, be readily implemented by practitioners in this field.

Claims

CLAMS:

1. A fuel injection nozzle comprising: a nozzle body defining a nozzle axis, said body having a seat and at least one discharge orifice at one axial end, a valve chamber centered on said axis and extending between the discharge orifice and the other axial end, and a fuel feed passage intersecting said valve chamber in said nozzle body; an elongated valve slidable axially in said valve chamber; a nozzle holder secured to said nozzle body, said nozzle holder including means for biasing the valve into contact with the seat and another fuel feed passage connected to the fuel feed passage in the nozzle body; and means for maintaining a compression pre-stress on the nozzle body, acting radially inward toward said intersection of the fuel passage and the valve chamber.

2. The fuel injection nozzle of claim 1, wherein the nozzle body has a tapered exterior surface located laterally of said intersection, and the means for maintaining a compression pre-stress, maintains a force normal to said taper surface.

3. The fuel injection nozzle of claim 1, wherein said means for maintaining a pre-stress comprises a metal ring heat-shrunk around the nozzle body substantially laterally of said intersection.

4. The fuel injection nozzle of claim 2, wherein said means for maintaining a pre-stress comprises a metal ring heat-shrunk around the nozzle body substantially laterally of said intersection.

5. The fuel injection nozzle of claim 1, wherein said valve chamber includes an enlarged sump in the valve body, and said fuel passage intersects the valve chamber at said sump thereby forming a web between the valve chamber and fuel passage, and said tapered surface on the nozzle body is situated laterally of the sump.

6. A fuel injection nozzle comprising: a nozzle body defining a nozzle axis, said body having a discharge tip at one axial end, a valve guide at the other axial end, a valve chamber centered on said axis and extending between the valve guide and discharge tip, and a fuel feed passage extending longitudinally in the valve guide and intersecting said valve chamber in said valve guide; an elongated valve slidable axially in said valve chamber; a nozzle holder secured to said valve guide, said nozzle holder including means for biasing the valve into seating contact with the discharge tip and another fuel feed passage connected to the fuel feed passage in the valve guide; and means for maintaining a compression pre-stress on the valve guide, acting radially inward toward said intersection of the fuel passage and the valve chamber.

7. The fuel injection nozzle of claim 6, wherein said valve guide has a tapered exterior surface located laterally of said intersection, said nozzle holder is secured to the valve guide by a retaining nut having one end engaging threads on said nozzle holder and another end applying an axially directed clamping force on the valve guide; and said means for maintaining a compression pre-stress, comprises a tapered surface urged by said retaining nut against the tapered surface on the valve guide.

8. The fuel injection nozzle of claim 7, wherein the tapered surface for maintaining said prestress is formed as an angled interior shoulder on the other end of the retaining nut.

9. The fuel injection nozzle of claim 7, wherein the tapered surface for maintaining said pre-stress is formed by a ring having an angled interior shoulder, and said other end of the retaining nut draws said ring tapered surface against said valve guide tapered surface.

10. The fuel injection nozzle of claim 7, wherein the taper angle is in the range of 10 -60 from a reference plane perpendicular to said axis.

11. The fuel injection nozzle of claim 10, wherein the tapered surfaces are angled in the range of 30"-45".

12. The fuel injection nozzle of claim 7, wherein, said valve chamber includes an enlarged sump in the valve guide and said fuel passage intersects the valve chamber at said sump, thereby forming a web between the valve chamber and the fuel passage, and said tapered surface on the valve guide is situated laterally of the sump.

13. The fuel injection nozzle of claim 8, wherein the other end of the retaining nut includes an exterior surface for axially clamping the nozzle into a receiving socket in the cylinder head of an internal combustion engine, and means are operatively connected to the nozzle holder, for clamping said retaining nut axially in said socket.

14. The fuel injection nozzle of claim 8, wherein said retaining nut applies a clamping force perpendicular to said tapered surfaces, in the range of 3,000-6,000 Ibs.

15. The fuel injection nozzle of claim 14, wherein said retaining nut applies a clamping force perpendicular to said tapered surfaces, in the range of 3,000-6,000 Ibs.

16. The fuel injection nozzle of claim 15, wherein said nozzle is clamped to a socket in the cylinder head of an intemal combustion engine, with a clamping force against said socket, in the range of about 2,000-5,000 Ibs.

17. In a fuel injection nozzle having a nozzle body defining a nozzle axis passing through upper and lower ends of the body, at least one bore penetrating the upper end of said body and extending in a generally longitudinal direction into the interior of the body, an elongated valve slidable axially in one of said bores, a nozzle holder in registry with the upper end of said nozzle body, said nozzle holder including means for biasing the valve toward the lower end of the nozzle body, and a retaining nut for drawing the nozzle body toward the nozzle holder along said axis, wherein the improvement comprises: said retaining nut including means for generating a radially inward force component to compressively pre-stress the interior of the nozzle body around said at least one bore, as the retaining nut draws the nozzle body axially toward the nozzle holder.

18. The fuel injection nozzle of claim 17, wherein said nozzle body has an exterior tapered shoulder and the retaining nut has an inwardly tapered shoulder mating with the shoulder on the nozzle body, such that as the nozzle body and nozzle holder are drawn toward each other, the tapered surfaces transmit a longitudinal clamping force component parallel to the axis, for drawing the body and holder together, and an inward force component directed radially toward said axis, for generating said compressive pre-stress.

19. The fuel injection nozzle of claim 18, wherein the tapered surfaces are angled in the range of 10 -60 relative to a reference plane passing perpendicularly through the axis.

20. The fuel injection nozzle of claim 19, wherein said taper angle is in the range of 30"-45".