JP4075645B2 - Oil pH sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an oil pH sensor used for measuring pH in oil. In particular, the present invention relates to an oil pH sensor suitable for measuring pH for detecting oil deterioration in a high temperature atmosphere such as engine oil in an automobile. Here, the case where it uses for the vehicle-mounted pH sensor for determining the deterioration degree of engine oil is taken as an example, but it is not restricted to this.
[0002]
That is, the present invention can be applied to a pH sensor for measuring the deterioration of oil such as fuel, hydraulic oil, and lubricating oil in the industry in addition to the on-vehicle pH sensor.
[0003]
[Prior art]
Engine oil in automobiles is exposed to high temperatures and high pressures, and further contaminated materials are mixed to promote deterioration. This oil deterioration increases the resistance of each moving part of the engine, causes a decrease in engine performance and promotes wear. For this reason, the engine oil is usually exchanged every predetermined distance.
[0004]
However, deterioration of engine oil is also affected by oil type, operating conditions, engine usage time, outside air temperature, etc., and is not always proportional to the travel distance. For this reason, it is not always performed when the engine oil is optimally changed. It should be noted that, even in the same type of engine oil, various types of engine oil are supplied from each manufacturer by changing the quality of the oil and the formulation of additives such as antioxidants.
[0005]
Therefore, a method for judging the degree of oil deterioration by immersing the electrode directly in oil and measuring changes in electrical characteristics such as potential difference (changes with pH) for the purpose of oil exchange at the optimum time. Has been proposed (Patent Document 1, etc.).
[0006]
The above-described method for electrically measuring the degree of deterioration of oil is to measure the degree of deterioration of oil based on the difference in pH. Oil has a high hydrogen ion concentration due to a chemical change of an additive such as an antioxidant and an oxidation of the oil itself, resulting in a decrease in pH (-log [H]).
[0007]
For example, Patent Document 1 describes the following in the technical field related to automatic replacement of engine oil.
[0008]
The degree of deterioration of the oil is detected through the pH of the oil by a pH sensor provided in the oil pan. Then, it is determined when the alkalinity (pH) of the oil has dropped below a predetermined value, and the oil is removed and the oil is changed.
[0009]
The above publication does not specifically disclose what pH sensor is used.
[0010]
In general, a pH sensor has a configuration in which a reference electrode and a working electrode are directly immersed in oil and a potential difference thereof is measured (see Patent Documents 2, 3, 4, etc.).
[0011]
For this reason, there is a problem that the potential on the reference electrode side is not constant depending on the type of oil. On the working electrode side, even if the oil composition is the same, it varies depending on the manufacturer, and the oil absorbs moisture over time, so that the potential of the working electrode may not accurately correspond to the degree of deterioration.
[0012]
The relative dielectric constant of oil is usually as low as about 1.6 to 3. Generally, it can be handled in the same way as an aqueous solution with a relative dielectric constant of 35 or more, and a solvent having a high relative dielectric constant (ε = 78.5) such as water. This is because the influence of the mixed solvent on the ions (solvation state) is not necessarily constant, and does not correspond to the degree of deterioration correctly.
[0013]
The present invention has been made in view of the above, and it is possible to accurately measure the degree of oil degradation even if the oil composition is different or the oil absorbs moisture over time. An object is to provide a sensor.
[0014]
In Patent Document 6, an electrode pair is arranged in a lumen sealed on the oil contact side with a separation membrane (hydrogen ion sensitive membrane such as Nafin (trade name of DuPont) that selectively permeates only hydrogen ions). At the same time, a sensor for detecting an electrical characteristic by enclosing a polar solvent having a high boiling point to which a supporting salt is added has been proposed.
[0015]
However, this does not assume that the electromotive force due to the battery action between the reference electrode and the working electrode is measured like a pH sensor, and a voltage is applied between the electrode pair (usually the same metal material) in a polar solvent. It is applied to measure one or more of electrical characteristics such as electric resistance, dielectric constant, capacitance, etc., and is completely different from the present invention (page 8, page 8). (See lines 6-9).
[0016]
[Patent Document 1]
JP 56-47614 A [Patent Document 2]
JP-A-4-350552 [Patent Document 3]
Japanese Patent Laid-Open No. 5-005720 [Patent Document 4]
JP-A-5-281188 [Patent Document 5]
JP-A-6-201649 [Patent Document 6]
Copy of microfilm of Japanese Utility Model No. 2-80679 (Japanese Utility Model Application No. 4-38557)
[Means for Solving the Problems]
This invention solves the said subject with the pH sensor for oil of the following structure.
[0018]
A pH sensor comprising a reference electrode (comparison electrode) and a working electrode (response electrode) used for detecting the degree of deterioration in oil by pH measurement,
The reference electrode and the working electrode have a structure in which the liquid to be measured, the reference electrode, and the working electrode are partitioned by an electrically conductive partition plate, and
The working electrode is a polar resin / electrolyte complex composed of a polar resin and a polar solvent (electrolyte) with a high relative dielectric constant and a high boiling point to which a strong electrolyte is added. It is characterized by having.
[0019]
Here, since hydrogen ions in the test oil selectively reach the electrode body of the working electrode via an exchange resin (having ion selectivity), the oil type and the dielectric constant change (due to solvation, etc.) ) Is not affected. Moreover, since the reference electrode is separated by the working electrode and the electrically conductive partition plate, the reference electrode is not substantially affected by the hydrogen ion concentration acting on the working electrode or not at all. For this reason, stable detection of hydrogen ion concentration, that is, pH detection becomes possible.
[0020]
Moreover, the reason why a polar solvent having a high relative dielectric constant and a high boiling point is used as the polar solvent is that engine oil or the like is at a high temperature and ensures ionic conductivity (if the relative dielectric constant is small) The electrolyte does not ion dissociate.)
[0021]
In addition, when the reference electrode (comparative electrode) is directly immersed in oil,
(1) In the case of new oil: The difference in the oil type is the difference in the chemical species of the oil, and the non-constant environment causes the reference electrode to be different.
[0022]
(2) In the case of deteriorated oil: The chemical species constituting the deteriorated oil differ depending on the process of deterioration, which causes the potential of the reference electrode to be different.
[0023]
Therefore, isolating the reference electrode from the oil leads to stabilizing the potential of the reference electrode.
[0024]
Also in the working electrode (response electrode), the electrode potential is affected by how the solvent solvates with ions liberated from the electrode surface. Fig. 4 shows the relationship between the solvent ratio of the mixed solvent and the solvation in the homo-selective solvation and the hetero-selective solvation (Viktor Gutmann, "Donor and Acceptor" Society Publishing Center, 1983.3.10, p145 figure). (Quoted from 9-5). It is considered that the relationship between the solvent ratio and the solvation deviates from the dotted line due to the solvation state being substantially selective solvation or heteroselective solvation, and the electrode potential of the working electrode becomes a cause of variation.
[0025]
Therefore, isolating the working electrode from the oil leads to a reduction in variation in potential of the working electrode.
[0026]
“Homo-selective solvation” refers to the case where a cation and an anion are selectively solvated by the same solvent component, and “heteroselective solvation” refers to the case where a cation and an anion are combined. The case where each is solvated by a different solvent.
[0027]
As the form of the polar resin / electrolyte complex, the cation exchanger is impregnated with a high-boiling polar solvent in which a cation is added, or the cation exchange membrane is not in contact with the oil to be measured. It is assumed that the polar solvent is retained so that
[0028]
The above polar solvent having a high relative dielectric constant and a high boiling point refers to a polar solvent having a relative dielectric constant of 35 or more and a boiling point of 150 ° C. or more. Specifically, N, N-dimethylacetamide, N, N-dimethylformamide, One or two or more solvents selected from the group of dimethyl sulfoxide and propylene carbonate can be suitably used.
[0029]
Moreover, as a form of a plate-shaped ion permeable body, a plate-shaped ion permeable body is usually a porous plate-shaped body or a semipermeable membrane having a pore diameter of 10 to 100 μm.
[0030]
As a form of the plate-like conductor, there is one in which a current-carrying portion made of a highly conductive noble metal is exposed on both surfaces of the insulating plate-like body.
[0031]
Further, a general-purpose silver / silver chloride electrode is usually used as the reference electrode.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
1A and 1B show an embodiment of the pH sensor of the present invention.
[0033]
The pH sensor of the present embodiment basically includes a working electrode (response electrode) 11 and a reference electrode (comparison electrode) 13 that are used to detect the degree of deterioration in oil by pH measurement. .
[0034]
The working electrode 11 and the reference electrode 13 are isolated by being electrically connectable via a plate-like ion permeable body (filter) 15.
[0035]
Here, as the ion permeator 15, it is possible to transmit ions (conductive medium) in the electrolytic solution (ion-added polar solvent), and if it has an effect of not mixing the electrolytic solution between both electrodes more than necessary, It does not specifically limit, It is set as the perforated board or semipermeable membrane with a hole diameter of 10-100 micrometers. Here, the material of the perforated plate is usually plastic, but it may be a non-conductor such as glass or ceramic, and may further be a metal conductor. In addition, the ion permeable body 15 does not need to be an ion permeable part entirely, and may form an ion permeable part (liquid junction part) partially.
[0036]
The working electrode 11 is a polar resin / electrolyte complex composed of a polar resin 17 and a polar solvent (electrolyte) having a high relative dielectric constant and a high boiling point to which a strong electrolyte is added, and surrounds the working electrode body 19. To have hydrogen ion selectivity.
[0037]
Here, the hydrogen ion selectivity refers to the property that the polar resin / electrolyte complex permeates (conducts) only hydrogen ions.
[0038]
The polar resin / electrolyte complex means a so-called polar polymer / inorganic salt / high-boiling-point solvent hybrid system. 3 ”The Society Publishing Center, May 10, 1990, p. 102-104).
[0039]
The polar resin (polar group-introducing resin) is not particularly limited as long as it has hydrogen ion selectivity (proton conductivity) when impregnated with an electrolytic solution, and may be polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, or the like. In FIG. 1, the cation exchange resin 17 is impregnated with an electrolytic solution (strong electrolyte added polar solvent).
[0040]
Here, it is generally desirable that the working electrode body 19 of the working electrode 11 is made of stainless steel, titanium or the like having excellent corrosion resistance (acid resistance).
[0041]
Further, as the cation exchange resin, a commercially available cation exchange resin such as “Diaion” (manufactured by Mitsubishi Kasei Co., Ltd.), “Rohm and Haas = Amberlite” (manufactured by Tokyo Organic Chemical Co., Ltd.), “Dawex” (manufactured by Dow Chemical Co., Ltd.), “Duolite” (manufactured by Sumitomo Chemical Co., Ltd.), and “Nafion” (PSF) manufactured by DuPont, which will be described later, can be used as appropriate. Among these, when a strongly acidic type is impregnated with a conductive electrolyte, it is desirable that the sensor has good reactivity. As a form of the ion exchange resin, a porous resin is usually used, but a gel type resin may be used. Furthermore, although it is a molded body in this embodiment, it may be filled with an ion exchange resin bead body or a membrane laminated body and covered with the ion permeable body.
[0042]
A polar solvent having a relative dielectric constant (ε) of 35 or more and a boiling point (bp) of 150 ° C. or more (preferably 160 ° C. or more) is used. If the relative dielectric constant is low, ion separation of the electrolyte becomes difficult, ion conductivity decreases, and pH measurement becomes difficult. On the other hand, if the boiling point is too low, the engine oil will boil when the temperature rises, and pH measurement will be difficult as well.
[0043]
Specific polar solvents include N, N-dimethylacetamide (ε: 38.9, bp: 163 to 165 ° C.), N, N-dimethylformamide (ε: 36.7, bp: 153 ° C.) dimethyl sulfoxide ( One or more solvents selected from the group of ε: 46.6, bp: 189 ° C.) and propylene carbonate (propylene carbonate) (ε: 64.9, bp: 240 ° C.) can be suitably used. In the above description, the relative dielectric constant and boiling point are shown before and after in parentheses for reference.
[0044]
And as a supply source of a cation, strong electrolytes, such as lithium chloride, potassium chloride, lithium chlorate, etc. can be used conveniently, for example, The addition amount shall be the quantity used as 4-6N (regulation).
[0045]
The reference electrode (comparative electrode) 13 is generally a general-purpose silver / silver chloride electrode, and the solvent of the electrolytic solution is the polar solvent. That is, the reference electrode body 20 in which an AgCl film is formed on the surface of an Ag plate (or Ag bar) is surrounded by a polar solvent having a high boiling point and a high relative dielectric constant containing chlorine ions. The reference electrode is surrounded by the electrode case 21 and the plate-like ion permeable body 15. The reference electrode is not limited to a silver / silver chloride electrode, and a platinum / iodine electrode or the like can also be used.
[0046]
The electrode case 21 is not particularly limited as long as it has good insulation and heat resistance, but is preferably formed (molded) with a heat resistant resin such as polyphenylene sulfide (PPS) or epoxy resin.
[0047]
At this time, as the chloride ion supply source, the above-described strong electrolyte such as lithium chloride or potassium chloride can be used. And let these addition amount be the quantity used as 4-6N (regulation). Also in the comparative electrode, as described above, a cation exchange resin may be impregnated with an electrolytic solution.
[0048]
The pH sensor shown in FIG. 2 is a modification of FIG. 1, in which the electrically conductive partition plate is a plate-like conductor 16. The whole may be a conductor, but from the viewpoint of electrical resistance, What exposed both sides of the electricity supply part 16b which consists of a highly conductive noble metal (platinum, silver, gold | metal | money etc.) in the center of the board | plate material 16a of material is desirable. Here, the precious metal is used because the precious metal does not corrode.
[0049]
Further, in the embodiment shown in FIG. 3, the polar resin / electrolyte complex is not in contact with the oil to be measured by the cation exchange membrane 18 and has a high dielectric constant and high boiling point electrolyte (electrolyte-added polar solvent). ) 23 is held. Here, the polar solvent, the electrolyte, and the reference electrode are the same as those in FIG.
[0050]
As the cation exchange membrane (ion selective membrane) 18, a polyperfluorocarbon-based polyanion (polyperfluorosulfonic acid: PSF) such as “Nafion” (PSF) manufactured by DuPont can be suitably used.
[0051]
Next, how the pH sensor is used will be described.
[0052]
Although not shown, the pH sensor of the present invention is usually installed in a test oil tank that can introduce oil attached to the bottom of an oil pan. The working electrode 11 of the pH sensor and the lead-out terminals 11a and 13a of the reference electrode 13 are connected to the display circuit 27 via the measurement circuit 25, and the alkalinity (pH) of the oil has dropped below a predetermined value. Sometimes it is displayed (output) by an oil warning or the like.
[0053]
At this time, the hydrogen ion concentration (pH) in the oil acts on the working electrode 11 through an ion exchange resin body (membrane) having hydrogen ion selectivity, and therefore, the influence of the type of oil and oil absorption. Stable pH detection is possible without being affected by changes in dielectric constant. Therefore, it is suitable as a pH sensor for detecting oil deterioration in automobiles.
[Brief description of the drawings]
1A and 1B are a vertical schematic cross-sectional view and a horizontal schematic cross-sectional view showing an embodiment of a pH sensor according to the present invention. FIG. 2 is a vertical schematic cross-sectional view showing a modification of the pH sensor of FIG. FIG. 3 is a schematic cross-sectional view showing another embodiment of the pH sensor according to the present invention. FIG. 4 is a graph showing examples of homo-selective solvation and hetero-selective solvation.
11 Working electrode (response electrode)
13 Reference electrode (reference electrode)
15 Plate-shaped ion permeator (plate-shaped conductive partition plate)
16 Plate-shaped conductor (plate-shaped conductive partition plate)
17 Cation Exchange Resin 18 Cation Exchange Resin Membrane 19 Working Electrode Body 20 Reference Electrode Body 21 Electrode Case 23 Electrolyte

Claims (8)

A pH sensor comprising a reference electrode (comparison electrode) and a working electrode (response electrode) used for detecting the degree of deterioration in oil by pH measurement,
The reference electrode and the working electrode have a structure partitioned by an electrically conductive partition plate, and
The working electrode is a polar resin / electrolyte complex composed of a polar resin and a polar solvent having a high relative dielectric constant and a high boiling point to which a strong electrolyte is added, and has hydrogen ion selectivity by surrounding the electrode body. An oil pH sensor.   The pH sensor according to claim 1, wherein the polar resin / electrolyte complex is a cation exchanger impregnated with a polar solvent having a high relative dielectric constant and a high boiling point. Claim 1, wherein the polar resin / electrolyte complex, and characterized in that the high-boiling polar solvent high specific dielectric constant such that the measured oil and non-contact with a cation exchange membrane is held The pH sensor for oil described .   The oil pH sensor according to claim 1, wherein the polar solvent is formed of a cation exchange resin having a relative dielectric constant of 35 or more and a boiling point of 150 ° C or more.   The said polar solvent consists of 1 type, or 2 or more types of solvents selected from the group of N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, and propylene carbonate. Oil pH sensor.   The oil pH sensor according to claim 1, wherein the electrically conductive partition plate includes an ion permeable portion.   The oil pH sensor according to claim 1, wherein the electrically conductive partition plate includes an energization portion.   The oil pH sensor according to claim 1, wherein the reference electrode is a silver / silver chloride electrode.

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