SILICON MICROMACHINED COMPOUND NOZZLE

Abstract: A silicon compound nozzle has two generally planar parallel plates (10,30) with offset openings (11,12,13,14 and 31) coupled by a shear gap (32). Fluid flow in the shear gap (32) is generally parallel to the plates (10,30) and increased fluid dispersion.

Description: This invention relates to micromachined silicon nozzles. Silicon nozzles of various types are known for controlling fluid flow. For example, U.S. Patent No. 4,007,464 issued to Bassous teaches the use of a single silicon plate with openings therethrough for controlling fluid flow. U.S. Patent N. 4,628,576 issued to Giachino et al and assigned to the assignee hereof teaches a valve wherein two silicon plates move with respect to each other and control fluid flow through an opening in one of the silicon plates. US-A-4,647,013 discloses a silicon valve structure including a first planar silicon member having a central mesa a sectional wall paramater and supply passages formed in the wall parameter. The valve structure further includes a second planar silicon member having a nozzle orifice aligned with the central mesa of the first member. The valve operates by positioning the first member adjacent the second member so that the mesa covers the orific. When the first member is deflected and the mesa is spaced from the orifice, fluid can flow from the supply passages between the portion of the wall parameter and out through the nozzle of the second member. In applications such as injecting fluid into combustion cylinders it is often desirable to have a very fine atomised dispersed fuel spray. Although known nozzles provide some such atomisation, improvements would be desired. Further, it would be desired to have a relatively simple nozzle structure which is easily fabricated to produce such a spray. These are some of the problems which this invention overcomes. According to the invention there is provided a silicon compound nozzle for guiding fluid flow, the nozzle including a generally planar first silicon plate having a first opening, a generally planar second silicon plate adjacent and parallel to said first silicon plate and having a second opening formed therethrough, characterised in that said first opening is formed through the first plate and is offset from said second opening in said second silicon plate, and in that said silicon compound nozzle having a first area of reduced thickness between said first and second openings so as to form a first shear gap for fluid flow substantially parallel to the plane of said first and second plates. Such shear flow causes turbulence and fluid dispersion advantageous for atomizing fuel in a combustion cylinder. In one embodiment, two shear flows are opposed to each other and collide so as to increase fluid dispersion. A nozzle in accordance with an embodiment of this invention is advantageous because it is relatively easily fabricated using silicon micromachining techniques and produces a fluid flow with a high velocity exiting characteristic. The invention will now be further described by way of example with reference to the accompanying drawings in which: Figure 1 is a plan view of a compound nozzle assembly in accordance with an embodiment of this invention; Figure 2 is a section along 2-2 of Figure 1; Figure 3 is a perspective, partly broken away view of the nozzle assembly of Figure 1; Figure 4 is a top perspective view of the flow plate of the nozzle assembly of Figure 3 in accordance with an embodiment of this invention; Figure 5 is a bottom perspective view of the flow plate of Figure 4 in accordance with an embodiment of this invention; Figure 6 is a top perspective view of the orifice plate of the nozzle assembly of Figure 3 in accordance with an embodiment of this invention; and Figure 7 is a perspective view of the bottom side of the orifice plate of Figure 6. Referring to Figures 1, 2 and 3, a compound silicon nozzle assembly includes a generally planar flow plate 10 cooperating with a generally planar orifice plate 30. Flow plate 10 is a symmetrical square silicon member with supply orifices 11, 12, 13 and 14 formed through flow plate 10 and positioned about the center of flow plate 10. Each opening has its longer side parallel to the closest edge of flow plate 10. As shown in Figures 2, 4 and 5 the surface of flow plate 10 facing orifice plate 30 has a generally rectangular annular trough 15 formed around a mesa 16 and spaced from the edges of flow plate 10. Figures 6 and 7 show orifice plate 30. A central exhaust orifice 31 is formed through the middle of orifice plate 30 and tapers so as to have increasing cross-sectional area with increasing distance from the top surface of orifice plate 30 which faces flow plate 10. A raised wall 33 extends around the edge of orifice plate 30. Wall 33 of orifice plate 30 abuts the perimeter portion of flow plate 10 adjacent trough 15. A recessed shear orifice portion 32 of orifice plate 30 is bounded by wall 33 so that when orifice plate 30 is placed adjacent to flow plate 10, orifice plate 30 does not touch flow plate 10 within the boundaries of wall 33. Referring to Figure 2, exhaust orifice 31 of orifice plate 30 is aligned with flow mesa 16 of flow plate 10. Recessed shear orifice portion 32 spaces adjacent surfaces of orifice plate 30 from flow plate 10. Each of supply orifice 11, 12, 13 and 14 acts in conjunction with trough 15 to provide a fluid flow to shear orifice portion 32 and then through exhaust orifice 31 thereby passing through the combination of flow plate 10 and orifice plate 30. As can best be seen in Figure 2, the size of exhaust orifice 31 adjacent mesa 16 is smaller than the size of mesa 16. A shear gap is formed to the extent to which mesa 16 extends over shear orifice portion 32 of orifice plate 30. For example, after fluid flow enters supply orifice 14 it enters trough 15 and has a generally horizontal flow adjacent shear orifice portion 32 before passing through exhaust orifice 31. To fabricate the compound nozzle assembly, two separate silicon plate configurations are micromachined and then bonded together. Fabrication includes known masking techniques of silicon wafers which are then exposed to etching to produce the orifices. The tapering nature of the orifices is a result of etching from one side. A typical taper is the etch angle for silicon material with a 〈100〉 crystallographic orientation. Double tapers, such as found in the combination of trough 15 and supply orifices 11, 12, 13 and 14 are the result of double sided etching. Mesa 16 is formed by masking and protecting the mesa area during etching. Similarly, wall 33 is formed by masking and protecting the area of wall 33 during etching of shear orifice portion 32. Shear orifice 32 and exhaust orifice 31 are etched from opposing sides so that they have opposing tapers. The fluid shear gap is produced by the overlap of the mesa and the bottom plate adjacent the exhaust orifice. This gap determines the flow rate and dispersion characteristics of the nozzle for fluid flow at a given pressure.

Claims: A silicon compound nozzle for guiding fluid flow, the nozzle including a generally planar first silicon plate (10) having a first opening (11,12,13,14), a generally planar second silicon plate (30), adjacent and parallel to said first silicon plate (10) and having a second opening (31) formed therethrough, characterised in that said first opening (11,12,13,14) is formed through the first plate (10) and is offset from said second opening (31) in said second silicon plate (30), and in that said silicon compound nozzle having a first area of reduced thickness between said first and second openings so as to form a first shear gap for fluid flow substantially parallel to the plane of said first and second plates (10,30). A silicon nozzle as claimed in claim 1 further comprising a third opening (12) in said first plate (10) offset from said first opening (11) said third and second openings being offset from each other and acting in co-operation with a second area of reduced thickness between said third and second openings in said silicon compound nozzle forming a second shear gap for fluid flow substantially parallel to the plane of said first and second plates (10,30). A silicon nozzle as claimed in claim 2 further comprising a fourth opening (13) in said first plate (10) offset from said first, second and third openings and acting in co-operation with a third area of reduced thickness between said fourth and second openings in said silicon compound nozzle forming a third shear gap for fluid flow substantially parallel to the plane of said first and second plates. A silicon nozzle as claimed in claim 3, wherein said first plate contains four generally rectangular openings (11,12,13,14) positioned around a central mesa area (16), said central mesa area (16) being aligned with said second opening (31) in said second plate (30) and said first, second and third shear gaps being defined by the surface of said mesa (16) and the adjacent surface of said second silicon plate (30). A silicon nozzle as claimed in claim 4, wherein the extent of the shear gap overlap between said mesa (16) and said second silicon plate (30) adjacent said second opening (31) is relatively small compared to the size of said second opening. A silicon nozzle as claimed in claim 5, wherein the surface of said second silicon plate (30) facing said first silicon plate (10) has a recess adjacent each opening in said first silicon plate. A silicon nozzle as claimed in claim 6, wherein said first plate (10) includes an annular recess around said central mesa, said recess being aligned with each of said openings (11,12,13,14) in said first plate (10). A silicon nozzle as claimed in claim 7, wherein each of said openings (11,12,13,14) in said first plate tapers and decreases in cross sectional area with decreasing distance to said second plate (30). A silicon nozzle as claimed in claim 8, wherein said annular recess in said first (10) plate tapers and decreases in cross sectional area with increasing distance from said second plate (30).

Inventors: GARDNER, ROBERT CLIFFORD, HORN, WILLIAM FREDERICK, RHOADES, MARK DEVIN, WELLS, MARVIN DUANE, YOCKEY, STEVE JOHN
Applicants: FORD FRANCE S. A., FORD MOTOR COMPANY, FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT
Application year: 1989
Main classification: B05B1
IPC codes: F02M61, B41J2, B05B1