A LIQUID MIXTURE RATIO DETECTOR DEVICE

Abstract: In a mixing liquid ratio detector device, a LED and a photo diode are provided in a manner to sandwich an optically permeable column. The light emittiung area of the LED and the light receiving area of the photo diode are each arranged in the neighbourhood of the column in generally perpendicular relationship with a boundary between a mixing liquid and the column, such that light beams from the LED enter the boundary through one side of the column, the light beams incident on the boundary at an angle more than a critical angle being totally reflected from the boundary, and advancing through an inner portion of the column to come out from the other side of the column, and impinging on the photo diode.

Description: This invention relates to a liquid mixing sensor which optically detects the mixing ratio of a liquid mixture which includes at least two liquid components. In internal combusion engines, mixtures of gasoline and alcohol have been employed as substitutes for gasoline. These substitute fuels necessitate the provision of a detector device which continuously or quasi-continuously detects the mixing ratio of gasoline and alcohol to obtain an appropriate air-fuel ratio and ignition timing. As seen in Fig. 5a, a prior art detector device has an optically permeable member 720a, a bottom surface 722 of which is brought in contact with a liquid mixture 790 composed of gasoline and alochol. The member 702a is enclosed in a casing filled with an epoxy mould resin 720 to form an optically permeable column 702. A LED 704 and a photo diode 705 are embedded into the epoxy mould resin 720 in parallel overlying relationship to the bottom surface 722. Some of the light beams from the LED 704 are incident on the bottom surface 722 at more than a critical angle, and undergo total internal reflection from the bottom surface 722 so as to impinge on the photo diode 705 which produces an output according to the intensity of the light beams impinging thereon. In this device, however, the light receiving area of the photo diode has to increase to account for a greater angle of incidence on the column 702, or else it is necessary to choose a greater distance between the photo diode 705 and and the LED 704, which causes the scale of the device to be greater. In addition, since it is necessary that the photo diode 705 and the LED 704 be located in the mould resin 720, it is difficult to mould resin which has optimal characteristics for all relevant factors such as adhesion, expansion, refraction, transparency and endurance. Therefore, it is an object of the invention to provide a detector device which has a long service life with low costs of manufacture, small size and high precision. Further, another example of a prior detector device (D) is shown in Fig. 5. This device carries a trapezoidal prism 200 disposed to have a boundary with a fuel mixture 110. A LED 300 and a photo diode 400 are placed on either side of the prism 200. However, the detector device (D) has the following drawbacks. The trapezoidal prism is costly with insufficient compensation which is required due to temperature effects and deterioration of the LED, thus leading to loss of precision. Even recently introduced detector devices have the following drawbacks: The height of the optical permeable column is great causing the device to be heavy. The light receiving area of the photo diode is great because a broad range is required for the light beams to impinge on the photo diode. Therefore, the invention has its object to provide a liquid mixture ratio detector device which is capable of reducing the drawbacks mentioned above, which accurately detects the mixing ratio with a lightweight column and small-scale light receiving elements because light receiving and light emitting diodes are disposed in a gel-like filler. DE - 2224310 teaches the use of a glass column and detectors and emitters placed about the column to detect the a liquid mixture ratio. The pre-characterising portion of the claim has been based on this disclosure. According to the invention there is provided a liquid mixture ratio detector comprising: an optically permeable column, having a bottom surface which in use is in contact with a liquid, and forms a boundary between the liquid and the bottom surface of the column; light emitting and light receiving elements disposed about the column such that in use optical paths are formed from the light emitting element, passing into the column, onto the boundary, out of the column and to the light receiving element, which produces an output according to the intensity of the light beams impinging thereon; characterised in that the light emitting area of the light emitting element and the light receiving area of the light receiving element are substantially perpendicular to the boundary. Preferably, the light receiving and light emitting elements are disposed to opposite sides of the column. Advantageously, the light beams reflected by the boundary pass through the column and leave the column partly from the side of the column, and partly from the upper surface of the column. Further, a transparent filler may be disposed to fill between the light emitting element and the column, and also between the light receiving element and the column, the refractive index of the filler being chosen in relation to that of the column. Preferably, the transparent liquid filler has a lower refractive index than the column while all the light beams incident on the boundary at more than a critical angle are adapted to come out from the other side of the column. With this arrangement it is unnecessary to make all the light beams reflected by the boundary come out from the side of the column, thus allowing the axial dimension of the column to be reduced. Alternatively the filler may be chosen to have a lower refractive index than the column, thus controlling dispersion of the light beams which impinge on the light receiving element. The column may be adapted so that light reflected from the boundary leaves the column only by its side and not its top in order to prevent internal reflection from the top of the column. The invention will be further described by way of non-limitative examples with reference to the accompanying drawings in which: Fig. 1 is a cross sectional view of a liquid mixture ratio detector device according to a first embodiment of the invention; Fig. 2 is a perspective view of an alternative form of column; Fig. 3 is a perspective view of another alternative form of column; Fig. 4 is a schematic view depicted for the purpose of explaining operation; Fig. 5 is a view of a prior art detector device; Fig. 5a is a schematic view of an other prior art detector device depicted for the purpose of comparing it to the device according to the present invention; Fig. 6 is a cross-sectional view of a mixing liquid ratio detector device according to a second embodiment of the invention; Fig. 7 is a cross-sectional view of the detector device of Fig. 6 with optical path depicted; Fig. 8 is an explanatory view for showing how the light beams refract at the corner of the column; and Fig. 9 is a view similar to Fig. 6 according to a third embodiment of the invention. Now a first embodiment of the invention is described with reference to Fig. 1. A detector device (C) is installed at an opening 792 provided in a pipe 791 through which a liquid fuel mixture 790 of gasoline and alcohol flows. The liquid fuel mixture 790 may be combination of gasoline with ethanol, butanol, methanol or a more highly polymerized alcohol. Alternatively, the combination may be alcohol and kerosene. Around the periphery of the opening 792, a cylindrical holder 701 is attached which has a lid at its upper open end, and at the same time, has a flange 711 fixed to the pipe 791. Into the holder 701, a glass column or plate 702 is inserted and the holder rendered impermeable by means of O-ring 793. The lower surface 722 of the column contacts the liquid fuel mixture 790. In this instance, the glass column 702 is in contact with the lower face of the upper lid of the holder 701. The glass column 702 is made of flint glass and is cylindrical as seen in Fig. 2, and has a refractive index of 1.55. The column may be rectangular as seen at 702A in Fig. 3. Between the column 702 and an inner surface 712 of the holder 701, an annular space (Ap) is provided into which base plates 706, 706a are located in opposed relationship with the column 702 interposed therebetween. The base plate 706 has a light emitting diode 704, and base plate 706a a photo diode 705 together with a compensation diode; all three diodes are coated with silicone resin 707. Both light emission and light receiving areas of the three diodes 705, 705a, 704 are perpendicular to the boundary between the lower face of the column and the liquid fuel mixture 790. The light emitting diode 704 is of Ga-As type, and emits infrared rays 741 when energized. The infrared rays 741 enter the column 702 through the annular space (Ap). The rays 741 incident on the bottom 722 at more than a critical angle are totally internally reflected from the boundary and come out of the column 702. The rays 741 impinge on the photo diode 705 which produces an output representative of the intensity of the rays 741 impinging thereon. The amount of rays 741 impinging on the photo diode 705 changes in accordance with the critical angle at which the rays 741 are reflected from the boundary 722. The output of the diode allows a combustion control device to determine the most appropriate ignition timing and air to fuel ratio. Upright members 716a, are terminal electrodes for output or input. With the structure thus far described, it is possible to provide a compact and endurable detector device (C) with low cost, but high detecting precision. The prior art device of Fig. 5a will be compared with the schematic view in Fig. 4 of the first embodiment of the invention. In Fig. 5a a dimensional relationship between (v₁), (ϑ) and (t₁) may be expressed as follows: l₁ = 2t₁ tan ϑ; l₁ = 3.46t₁ when incident angle (ϑ) is 60 degrees. Where (l₁) represents the intended distance between the two diodes, while (t₁) represents the vertical distance between the boundary and the light emitting diode (photo diode). A differential equation dl₁ / dt₁ = 3.46 is obtained from the equation l₁ = 3.46t₁. Therefore, a dimensional inaccuracy in (t₁) affects the dimension of (l₁) by a factor of 3.46 which requires the light receiving area of the photo diode to be broad in order to absorb the dimensional error of (t₁). In Fig. 4 tan ϑ = D/(l₂ + t₂) and therefore (l₂) = 0.557D - t₂ when incident angle (ϑ) is 60 degrees, where (D) represents a distance between two diodes, while (l₂) and (t₂) in turn represent a distance between the point at which rays 741 impinge on the photo diode and the boundary, and a distance between the light emitting diode and the boundary. It can be inferred from the latter equation that the dimensional accuracy of (l₂) is less dependent on those of (t₂) and (D). Light emitting and light receiving areas of the light emitting diode and photo diode are arranged to be perpendicular to the boundary (722), so that the angle of incidence on the side wall of the column becomes small e.g. 30° even when the critical angle of incidence on the boundaray 722 is somewhat greater e.g. 60°. The angle of refraction as the rays 741 leave the column becomes small in the case above. This eliminates the need for a transparent filler between the light emitting photo diode and the wall of the column. It is noted that the column may be liquid-tightly sealed by means of a plate packing instead of O-ring. On the opposite surface from the outer bottom 722, the upper surface of the column may have an undulating heat transfer portion. It is further noted that space between the light emitting diode and the column wall may be filled with silicone or epoxy resin to prevent the surface of the diode from being fouled. In this instance, space between the photo sensitive diode and the circumferential wall may be filled with silicone or epoxy resin for the same purpose. This arrangement works to prevent the optical path from being significantly diverted even when the circumferential wall of the column is not smooth. Fig. 6 shows a second embodiment according to the invention which comprises a metallic holder 1 having a circular aperture 11 at its bottom. The device (A) further comprises a glass column 2 inserted into the aperture 11, a silicon-gel 3 applied to the holder 1, and a light emitting diode 4, a photo diode 5 together with a compensation photo diode 6 each disposed in the silicone-gel 3. A glass ring 7 is provided to bond the glass column 2 to the holder 1. O-ring 530 seals a passage between pipe 500 and the holder 1. The device (A) is installed on the pipe 500 through an opening 520 across which a liquid fuel mixture of gasoline and alcohol 510 (refractive index: 1.33-1.43) flows. The holder 1 is made of stainless steel. An annular space is provided between an end of the aperture 11 and an outer surface of the glass column 2 for securing the glass ring 7. On the upper surface 12 of the holder 1, a hollow cylinder 13 of synthetic resin is provided to surround the glass column 2 which is made of flint glass (refracting index: 1.58), and measures 8mm in diameter, and 2.5 mm in length (height). The column 2 has lower surface 21 which is immersed in the liquid fuel mixture of gasoline and alcohol 510 to form a boundary 21, has an upper surface 22 and a circumference 23 around which is provided the glass ring 7. The silicone-gel 3 serves as transparent filler and has a refractive index of 1.40, and extends to the upper open end of the cylinder 13. A light emitting diode 4 (LED) is attached to an inner wall of the cylinder 13, and its upper extent falls somewhat below an extension line (E) of the upper surface 22 of the column 2. The photo-sensitive diode 5 is attached to the inner wall of the cylinder 13 so as to oppose the light emitting diode 4 beyond the glass column 2 and its upper and lower extents straddle the extension line (E). The compensation photo diode 6 is installed on the inner wall of the cylinder 13 directly below the photo diode 5. The glass ring 7 is made of flint glass having height of 1 mm, and thickness of 1 mm. The melting point of the glass ring 7 is lower than that of the glass column 2. The glass ring 7 supports the glass column 2 to maintain the outer bottom (boundary) 21 immersed in the liquid fuel mixture of gasoline and alcohol 510. The height and diameter dimensions of the column 2, and the vertical position of photo diode 5 are determined such that light beams from the light emitting diode 4 enter into one side of the column 2 through the transparent liquid filler (silicone-gel) 3 to be incident on the boundary 21. The light beams incident on the boundary at an angle more than a critical angle are totally reflected from the boundary 21, and advance through the column 2 to leave partly from the other side of the column 2 as seen at an optical path 41 in Fig. 7, and partly coming out from an upper surface 22 of the column 2 through the silicone gel 3 as seen at an optical path 42 to impinge on the photo diode 5 so as to produce an output according to the light beams impinging thereon. It is noted that a vertical range as designated at 43 is variable corresponding to upper and lower limits of alcohol content in the liquid fuel mixture 510. A change of the mixing ratio of the liquid fuel mixture 510 causes the critical angle to increase so that the upper extent of the spread of beams impinging on the photo sensitive diode 5 moves upwards. Fig. 8 shows how the optical refraction occurs at the upper surface 22. Since the refractive index of the glass column 2 is chosen to be greater than that of the silicone-gel 3, the light beams from the light emitting diode 4 are shown by the solid-lined optical path 42 when the incident angle (ϑ3) is smaller than the refraction angle (ϑ4). When the light beams come out of the column wall 23 to enter the silicone-gel 3, the relationship between the incident angle and the refraction angle is expressed by an inequality (ϑ1) < (ϑ2) as seen at broken lines 44. In cases in which it is necessary to let the light beams on path 42 come out of the wall 23 into the silicone-gel 3, the height of the column 2 is required to reach a level as seen at broken lines 24 in Figs. 7 and 8. The detector device according to the present invention has the following advantages. The glass column 2 is only required to be at least as high as is depicted by the solid line in Fig. 7 and 8, thus making it possible to provide a compact and light weight detector device (A). The light weight of the glass column 2 serves to assist in retaining the column bonded to the metallic holder 1. The solid-lined optical path 42 makes it possible to prevent the light beams from dispersing broadly, thus enabling the light receiving area of the photo diode to be relatively small leading to a compact diode at low cost. This effect is all the more enhanced as the difference in refractive indices between the silicone-gel 3 and the glass column 2 becomes greater. It is possible to make the height of the glass column 2 small so that the thermal stress from the glass ring 7 due to temperature change becomes minor so as to prevent cracks from occurring on the column 2. Fig. 9 shows a third embodiment of the invention. In a detector device (B) according to this embodiment, the compensation photo diode 6 is located somewhat above the photo diode 5. Some of the light beams from the light emitting diode pass directly through the silicone-gel 3 to impinge on the photo diode 5 without advancing into the glass column 2, as shown by optical path 45. This arrangement allows the light intensity of the light emitting diode to be monitored regardless of whether the mixing ratio of gasoline and alcohol changes. Further, this arrangement allows the prevention of light beams 45 from being occluded by the glass ring 7. The arrangement of the compensation photo diode 6 is substantially immune to the critical angle depending on the mixing ratio of gasoline and alcohol 510, thus the positioning the compensation photo diode 6 is not critical. It is appreciated that the mixing liquid to be detected may be mobile or stationary. Further, it is noted that the column may have the property that it resists erosion of the mixing liquid to be detected and may be of sodium glass, Pyrex glass, borosilicate glass or acryl synthetic resin. Furthermore, it is noted that the glass column plate may be polygonal or elliptic. It is also appreciated that the critical angle of incidence on the boundary may preferably by chosen to be more than 45 degrees for the sake of ready installation of the light emitting diode and the photo diode.

Claims: 1. A liquid mixture ratio detector comprising: an optically permeable column, having a bottom surface which in use is in contact with a liquid, and forms a boundary between the liquid and the bottom surface of the column; light emitting and light receiving elements disposed about the column such that in use optical paths are formed from the light emitting element, passing into the column, onto the boundary, out of the column and to the light receiving element, which produces an output according to the intensity of the light beams impinging thereon; characterised in that the light emitting area of the light emitting element and the light receiving area of the light receiving element are substantially perpendicular to the boundary. 2. A liquid mixture ratio detector according to claim 1 wherein the light receiving and light emitting elements are disposed to opposite sides of the column. 3. A liquid mixture ratio detector according to claim 1 or 2 wherein in use the light beams reflected by the boundary pass through the column and leave the column partly from the side of the column, and partly from the upper surface of the column. 4. A liquid mixture ratio detector according to claim 1, 2 or 3 wherein a transparent filler is disposed to fill between the light emitting element and the column, and also between the light receiving element and the column, the refractive index of the filler being chosen in relation to that of the column. 5. A liquid mixture ratio detector according to any of the preceding claims further comprising: a transparent filler disposed to fill between the light emitting element and the column, and at the same time, filling between the light receiving element and the column; the height and diameter dimensions of the column, and vertical position of the light receiving element being chosen such that light beams from the light emitting element enter one side of the column through the transparent filler to be incident on the boundary, the light beams incident on the boundary at an angle more than a critical angle being totally reflected by the boundary advancing through the column so as to come out partly from the other side of the column, and partly from an upper surface of the column to impinge on the light receiving element so as to produce an output according to the intensity of the light beams impinging thereon. 6. A liquid mixture ratio detector according to claim 5, the transparent liquid filler having a lower refractive index than the column while all the light beams incident on the boundary at more than a critical angle are adapted to come out from the other side of the column. 7. A liquid mixture ratio detector according to claim 5 or 6 including a holder for supporting the column.

Inventors: KIYOTAKA, OHNO, SHIGERU, MIYATA
Applicants: NGK SPARK PLUG CO., LTD
Application year: 1989
Main classification: F02D41
IPC codes: F02D41, G01N21