JP2013195160A - Fuel sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel sensor capable of improving detection accuracy.SOLUTION: An outside electrode 30 comprises: an outside insert part 31 inserted into a resin body 10; and an outside immersion part 32 protruding into a fuel passage from the resin body 10. An inside electrode 40 provided on an inner diameter side of the outside electrode 30 comprises: an inside insert part 41 inserted into the resin body 10; an inside immersion part 42 protruding into the fuel passage from the resin body 10; and a protrusion 43 protruding to the side opposite to the fuel passage 2 from the resin body 10. Detection means 51 detects alcohol concentration in fuel on the basis of capacitance between the electrodes. A first O-ring 61 fluid-tightly contacts an outside wall of the protrusion 43 of the inside electrode 40 and the resin body 10. Thereby, the detection circuit 51 can accurately detects the capacitance between the electrodes even when the first O-ring 61 causes positional deviation in an axial direction of the inside electrode 40.

Description

  The present invention relates to a fuel sensor that detects the properties of fuel.

2. Description of the Related Art Conventionally, a fuel sensor that is provided in a fuel supply system that supplies fuel to an internal combustion engine and detects a property of the fuel such as an alcohol concentration in the fuel is known. The alcohol concentration detected by the fuel sensor is transmitted to an electronic control unit (ECU) of the internal combustion engine. The ECU controls the fuel injection amount, fuel injection timing, ignition timing, and the like according to the alcohol concentration. As a result, the air-fuel ratio of the internal combustion engine becomes appropriate, the drivability is improved, and harmful components in the exhaust gas are reduced.
The fuel sensor described in Patent Document 1 includes a cylindrical outer electrode and an inner electrode provided inside the outer electrode. Fuel flows between the outer electrode and the inner electrode (hereinafter referred to as “between electrodes”). The detection circuit detects the alcohol concentration of the fuel based on the capacitance between the electrodes using the fuel as a dielectric.

JP2011-164085A

In the fuel sensor of Patent Document 1, the outer electrode is insert-molded in the housing, and the inner electrode is insert-molded in the holder. The holder is press-fitted and fixed inside the housing. Further, the O-ring provided between the outer electrode and the inner electrode in the fuel passage prevents the fuel flowing through the fuel passage from leaking to the detection circuit side through the gap between the housing and the holder.
However, in Patent Document 1, when the position of the O-ring provided between the electrodes shifts in the axial direction due to the vibration of the vehicle or the thermal contraction of the O-ring due to the temperature increase of the internal combustion engine, the outer electrode immersed in the fuel and The area of the inner electrode changes. In this case, the capacitance between the electrodes may change, and the detection accuracy of the fuel sensor may deteriorate.
Further, when the housing and the holder are displaced from each other, the outer electrode and the inner electrode are relatively displaced. In this case, the capacitance between the electrodes may change, and the detection accuracy of the fuel sensor may deteriorate.
The present invention has been made in view of the above problems, and an object thereof is to provide a fuel sensor capable of increasing detection accuracy.

The present invention relates to a fuel sensor in which an outer electrode and an inner electrode are inserted into a resin body, and an annular seal member is provided between the outer wall of the projecting portion of the inner electrode projecting from the resin body to the outside of the fuel passage and the resin body. It is characterized by closely contacting.
Thereby, a sealing member is provided in positions other than the immersion part which both electrodes immerse in a fuel. For this reason, when the seal member is displaced in the axial direction of the inner electrode, the electrical characteristics between the electrodes are not affected. Therefore, the detection means can accurately detect the electrical characteristics of the fuel flowing through the fuel passage, so that the detection accuracy of the fuel sensor can be improved.

It is sectional drawing of the fuel sensor by 1st Embodiment of this invention. It is a schematic diagram which shows the manufacturing method of the fuel sensor by 1st Embodiment of this invention. It is sectional drawing of the fuel sensor by 2nd Embodiment of this invention. It is sectional drawing of the fuel sensor by 3rd Embodiment of this invention.

Hereinafter, a plurality of embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
A fuel sensor according to a first embodiment of the present invention is shown in FIGS. The fuel sensor 1 according to the present embodiment is a sensor that is provided in a fuel passage 2 that connects a fuel tank of a vehicle and a fuel injection device, and detects a concentration of alcohol contained in the fuel.
As shown in FIG. 1, the fuel sensor 1 includes a resin body 10, an outer electrode 30, an inner electrode 40, a circuit board 50, a first O-ring 61 as a seal member, and the like.
The resin body 10 is made of, for example, resin and is attached to the opening 3 of the fuel passage 2. The resin body 10 includes a substrate housing portion 11 that houses the circuit board 50 outside the fuel passage 2, and an electrode support portion 12 that extends from the substrate housing portion 11 to the inside of the fuel passage 2. The electrode support portion 12 is molded with the outer electrode 30 and the inner electrode 40. The second O-ring 62 provided between the outer wall of the fuel passage 2 and the substrate housing portion 11 prevents the fuel flowing through the fuel passage 2 from leaking to the outside.

The outer electrode 30 is formed in a cylindrical shape from a metal such as stainless steel, and the central axis is provided substantially perpendicular to the fuel flow direction of the fuel passage 2. The outer electrode 30 includes an outer insert portion 31 that is inserted into the electrode support portion 12 of the resin body 10 and an outer immersion portion 32 that protrudes from the resin body 10 into the fuel passage. The outer immersion part 32 is immersed in the fuel flowing through the fuel passage 2.
In FIG. 1, the direction in which the fuel flows in the fuel passage 2 is indicated by arrows A and B.
The outer electrode 30 has an opening at the lower end 33 of the outer immersion part 32. The outer electrode 30 has a first flow hole 34 on the upstream side of the fuel flow, and a second flow hole 35 on the downstream side of the fuel flow. The fuel flows through the opening of the first circulation hole 34, the second circulation hole 35, and the lower end part 33 and inside the outer immersion part 32.

The outer electrode 30 has a flange 37 extending annularly in the radially outward direction at an upper end portion 36 located on the opposite side of the lower end portion 33. The flange 37 prevents the outer electrode 30 from moving in the axial direction or the radial direction with respect to the resin body 10.
The first terminal 71 connected to the flange 37 is electrically connected to the detection circuit 51 provided on the circuit board 50. The detection circuit of the present embodiment corresponds to “detection means” recited in the claims.
A wall 13 surrounding the first terminal 71 in a cylindrical shape is provided at a location where the first terminal 71 protrudes from the electrode support portion 12 to the inside of the substrate housing portion 11. An adhesive 14 is filled inside the surrounding wall 13. The adhesive 14 prevents the fuel from leaking out to the circuit board side from the gap between the first terminal 71 and the electrode support portion 12. Before the surrounding wall 13 is filled with the adhesive 14, a plasma surface treatment is performed on the inner wall of the surrounding wall 13. As a result, the inner wall of the surrounding wall 13 and the adhesive 14 are firmly bonded.

The inner electrode 40 is formed, for example, from a metal such as stainless steel into a bottomed cylindrical shape, and is provided substantially coaxially with the outer electrode 30 on the inner diameter side of the outer electrode 30. Between the outer wall of the inner electrode 40 and the inner wall of the outer electrode 30, a predetermined gap capable of detecting a capacitance using fuel as a dielectric is provided. The inner electrode 40 includes an inner insert portion 41 that is inserted into the electrode support portion 12 of the resin body 10, an inner immersion portion 42 that protrudes from the resin body 10 into the fuel passage, and a protrusion that protrudes from the resin body 10 to the opposite side of the fuel passage. Part 43. The inner immersion part 42 is immersed in the fuel flowing inside the outer immersion part 32.
A thermistor (not shown) can be installed inside the inner electrode 40. The thermistor detects the temperature of the fuel transferred from the inner electrode 40 and transmits a signal related to the temperature to the detection circuit 51.

The protruding portion 43 of the inner electrode 40 protrudes from the electrode support portion 12 to the circuit board side. The second terminal 72 connected to the protruding portion 43 is electrically connected to the detection circuit 51 provided on the circuit board 50.
The resin body 10 has a recess 15 that is recessed in an annular shape outside the diameter of the protrusion 43 of the inner electrode 40. A first O-ring 61 made of an elastic material such as fluorosilicone rubber is attached to the recess 15. The inner diameter of the recess 15 is set so that the first O ring 61 compresses the first O ring 61 to such an extent that the elastic force of the first O ring 61 can prevent fuel leakage from the gap between the inner electrode 40 and the resin body 10. . Therefore, the first O-ring 61 is in liquid-tight contact with the outer wall of the inner electrode 40 and the inner wall of the recess 15.
The first O-ring 61 is located closer to the circuit board than the flange 37 of the outer electrode 30. That is, the first O-ring 61 is attached to a place other than the position where the outer electrode 30 and the inner electrode 40 face in the radial direction. Accordingly, when the first O-ring 61 is displaced in the axial direction, the capacitance between the electrodes is not affected.

  A washer 80 as an annular member is provided on the circuit board side of the first O-ring 61. The washer 80 prevents the first O-ring 61 from moving in the axial direction of the inner electrode 40 and the first O-ring 61 from falling off the inner electrode 40. The washer 80 is embedded in the electrode support portion 12 of the resin body 10 by heat caulking.

  The circuit board 50 is accommodated in the substrate accommodating portion 11 of the resin body 10. The circuit board 50 includes a detection circuit 51 that detects the electrical characteristics of the fuel. The detection circuit 51 detects the capacitance between the electrodes using the fuel flowing inside the outer electrode 30 as a dielectric, by charging and discharging between the outer electrode 30 and the inner electrode 40. In the memory of the detection circuit 51, a calibration curve indicating the relationship between the alcohol concentration of the fuel and the capacitance is stored as a map corresponding to the fuel temperature. The detection circuit 51 detects the alcohol concentration contained in the fuel based on the calibration curve specified by the capacitance between the electrodes and the fuel temperature.

A method for manufacturing the fuel sensor 1 will be described.
First, the outer electrode 30 and the inner electrode 40 are insert-molded into the resin body 10. The outer insert portion 31 of the outer electrode 30 and the inner insert portion 41 of the inner electrode 40 are molded into the resin body 10.
Next, as shown in FIG. 2, the first O-ring 61 is fitted between the recess 15 of the resin body 10 and the protrusion 43 of the inner electrode 40. Then, the washer 80 is placed on the first O-ring 61.
Subsequently, as shown by an arrow C in FIG. 2, the cylindrical portion 16 extending upward from the electrode support portion 12 of the resin body 10 is bent inwardly by heat caulking. Thereby, the washer 80 is embedded in the resin body 10.
On the other hand, plasma surface treatment is performed on the inner wall of the surrounding wall 13, and then the adhesive 14 is filled inside the surrounding wall 13. Thereafter, the circuit board 50 is attached to the board housing part 11 of the resin body 10.

In the present embodiment, the following effects are obtained.
(1) In the present embodiment, the first O-ring 61 is provided between the protruding portion 43 of the inner electrode 40 and the resin body 10. As a result, even when the first O-ring 61 is displaced in the axial direction of the inner electrode 40, the depth at which the outer immersion portion 32 and the inner immersion portion 42 are immersed in the fuel does not change. For this reason, the displacement of the first O-ring 61 does not affect the capacitance between the electrodes. The fuel sensor 1 can accurately detect the electrical characteristics of the fuel. Therefore, the detection accuracy of the fuel sensor 1 can be increased.
(2) In the present embodiment, the first O-ring 61 is attached at a location away from the position where the outer electrode 30 and the inner electrode 40 face in the radial direction. Thereby, the 1st O-ring 61 does not affect the electrostatic capacitance between electrodes. Therefore, the detection accuracy of the fuel sensor 1 can be increased.
(3) In the present embodiment, the inner electrode 40 and the outer electrode 30 are insert-molded with one resin body 10. Thereby, the relative displacement of the inner electrode 40 and the outer electrode 30 is suppressed. Therefore, a change in capacitance between the electrodes is suppressed, and the detection accuracy of the fuel sensor 1 can be increased.
(4) In the present embodiment, the first O-ring 61 is attached to the recess 15 of the resin body 10. By setting the inner diameter of the concave portion 15 of the resin body 10, the compression rate of the first O-ring 61 can be adjusted. Therefore, it is possible to reliably prevent the fuel from leaking from the gap between the inner electrode 40 and the resin body 10 to the circuit board side.
(5) In this embodiment, the washer 80 is embedded in the resin body 10 by heat caulking. As a result, the first O-ring 61 can be prevented from falling off.

(Second Embodiment)
A fuel sensor according to a second embodiment of the present invention is shown in FIG. Hereinafter, in a plurality of embodiments, the same numerals are given to the composition substantially the same as a 1st embodiment mentioned above, and explanation is omitted.
In the second embodiment, the fuel sensor includes a passage member 20 constituting a fuel passage. The passage member 20 is formed of a conductor and includes a cylinder part 21, a bottom part 23, and a connecting pipe 22. The cylindrical portion 21 is provided in a cylindrical shape substantially coaxially with the outer electrode 30 in the radially outward direction of the outer electrode 30. The bottom portion 23 closes the opposite side of the cylindrical portion 21 from the resin body 10. The two connecting pipes 22 extend in a cylindrical shape in the radial direction of the cylindrical portion 21. In FIG. 3, the direction in which the fuel flows through the connecting pipe 22 is indicated by arrows A and B.
The third O-ring 63 provided between the inner wall of the cylindrical portion 21 of the passage member 20 and the electrode support portion 12 of the resin body 10 prevents the fuel flowing through the passage member 20 from leaking outside.

The third terminal 73 has one end connected to the flange 37, protruding from the resin body 10 in the fuel passage, and the other end connected to the passage member 20. A fourth terminal 74 connects the passage member 20 and the circuit board 50.
The inner electrode 40 has a groove 44 that is recessed in the radial direction on the circuit board side of the first O-ring 61. An E-ring 81 as a restricting means is locked in the groove 44 of the inner electrode 40. The E-ring 81 prevents the first O-ring 61 from moving in the axial direction of the inner electrode 40 and falling off from the inner electrode 40.

In the present embodiment, the passage member 20 and the outer electrode 30 have the same potential. Therefore, the distance L1 between the cylindrical portion 21 of the passage member 20 and the inner electrode 40 is long enough to ignore the influence of the stray capacitance between the cylindrical portion 21 and the inner electrode 40 on the alcohol concentration detection of the detection circuit 51. Is set to
The detection circuit 51 uses the outer electrode 30 and the passage member 20 as the ground, and the capacitance between the electrodes using the fuel flowing inside the outer electrode 30 as a dielectric by charging / discharging between the outer electrode 30 and the inner electrode 40. Is detected. The detection circuit 51 detects the alcohol concentration contained in the fuel based on the calibration curve specified by the capacitance between the electrodes and the fuel temperature.

In the second embodiment, the following effects are obtained.
(1) In the second embodiment, the E-ring 81 is locked in the groove 44 provided in the inner electrode 40. Thereby, the E ring 81 can be attached to the inner electrode 40 with a simple configuration.
(2) In the second embodiment, the third terminal 73 electrically connects the outer electrode 30 and the passage member 20 in the fuel passage. Thereby, it is possible to prevent the fuel from leaking from the connection portion between the outer electrode 30 and the detection circuit 51.
The third terminal 73 may connect the outer electrode 30 and the passage member 20 outside the resin body 10 in the fuel passage.

(Third embodiment)
A fuel sensor according to a third embodiment of the present invention is shown in FIG.
In the third embodiment, the outer electrode 30 includes a cylindrical small-diameter portion 301, a cylindrical large-diameter portion 302 having a larger diameter than the small-diameter portion 301, and a step portion connecting the small-diameter portion 301 and the large-diameter portion 302. 303. In the outer electrode 30, the portion of the small diameter portion 301 that protrudes from the electrode support portion 12 to the fuel passage constitutes the outer immersion portion 32.
The distance L2 between the large-diameter portion 302 and the inner electrode 40 of the outer electrode 30 is such that the influence of stray capacitance between the large-diameter portion 302 and the inner electrode 40 on alcohol concentration detection of the detection circuit 51 can be ignored. It is set to length. The large diameter part 302 protrudes from the electrode support part 12 of the resin body 10 to the circuit board side.

The resin body 10 has a second recess 17 that is recessed in an annular shape at a location where the large diameter portion 302 of the outer electrode 30 protrudes from the electrode support portion 12. A fourth O-ring 64 is attached between the outer wall in the radially outward direction of the large-diameter portion 302 and the second recess 17, and a fifth O-ring 65 is interposed between the inner wall in the radially-inward direction of the large-diameter portion 302 and the second recess 17. Is attached.
In the third embodiment, the fourth O-ring 64 and the fifth O-ring 65 can prevent fuel from leaking out from the gap between the large-diameter portion 302 of the outer electrode 30 and the resin body 10 to the circuit board side.

(Other embodiments)
The fuel sensors of the above-described embodiments detect the nature and state of the fuel from the dielectric constant of the fuel by detecting the capacitance between the electrodes. On the other hand, the fuel sensor of the present invention may detect the property and state of the fuel from the conductivity of the fuel by detecting the resistance value between the electrodes.
The fuel sensors of the above-described embodiments detect the concentration of alcohol contained in the fuel from the electrical characteristics between the electrodes. On the other hand, the fuel sensor of the present invention may detect, for example, the oxidative deterioration state of the fuel from the electrical characteristics between the electrodes.
The present invention is not limited to the above embodiment, and can be implemented in various forms without departing from the spirit of the invention.

DESCRIPTION OF SYMBOLS 1 ... Fuel sensor 10 ... Resin body 30 ... Outer electrode 40 ... Inner electrode 51 ... Detection circuit (detection means)
61 ... 1st O-ring (seal member)

Claims (9)

A fuel sensor (1) for detecting a property of fuel flowing in a fuel passage (2),
A resin body (10) attachable to the opening (3) of the fuel passage;
A cylindrical outer electrode (30) having an outer insert part (31) to be inserted into the resin body, and an outer immersion part (32) protruding from the resin body into the fuel passage;
An inner insert portion (41) to be inserted into the resin body, an inner immersion portion (42) protruding from the resin body into the fuel passage, and a protrusion portion (43) protruding from the resin body to the opposite side of the fuel passage. An inner electrode (40) provided on the inner diameter side of the outer electrode;
Detecting means (51) for detecting a property of the fuel based on an electrical characteristic of the fuel flowing between the outer electrode and the inner electrode;
A fuel sensor, comprising: an annular seal member (61) in liquid-tight contact with the outer wall of the protruding portion of the inner electrode and the resin body.   2. The fuel sensor according to claim 1, wherein an end portion (36) of the outer electrode opposite to the fuel passage is located closer to the fuel passage than the seal member.   3. The fuel sensor according to claim 1, wherein the resin body molds the outer side of the inner insert part and the inner side and the outer side of the outer insert part. 4.   The fuel sensor according to any one of claims 1 to 3, wherein the seal member is attached to a concave portion (15) of the resin body provided on a radially outer side of the protruding portion of the inner electrode. .   The fuel sensor according to any one of claims 1 to 4, further comprising limiting means (80, 81) for limiting the movement of the seal member in the axial direction of the inner electrode.   The fuel sensor according to claim 5, wherein the limiting means is an annular member (80) embedded in the resin body.   6. The fuel sensor according to claim 5, wherein the limiting means (81) is locked in a groove (44) provided in the inner electrode. A conductive passage member (20) constituting the fuel passage;
The fuel sensor according to claim 1, wherein the outer electrode is electrically connected to the passage member in the fuel passage. The passage member has a cylindrical portion (21) provided in a cylindrical shape in a radially outward direction of the outer electrode, and a bottom portion (23) that closes one of the cylindrical portions,
The distance (L1) between the cylindrical portion of the passage member and the inner electrode is such that the influence of stray capacitance between the passage member and the inner electrode on the property detection of the fuel performed by the detection means can be ignored. The fuel sensor according to claim 8, wherein the fuel sensor is set to a length.

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