JP2013083557A - Fuel sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel sensor capable of improving detection accuracy.SOLUTION: A fuel sensor is provided with a cylindrical outside electrode 30 in a fuel passage in which fuel flows. An inside electrode 40 is provided on the inner side in a diametrical direction of the outside electrode 30. A detection circuit detects electrical characteristics of the fuel flowing in an inner flow passage 41 formed between the outside electrode 30 and the inside electrode 40. The inside electrode 40 has a projecting portion 44 projecting from an outer wall in a diametrical outer direction toward the outside electrode 30. The outside electrode 30 has a recessed portion 34 positioned on the outer side in the diametrical direction of the projecting portion 44, and depressed from an inner wall of the outside electrode 30 in the diametrical outer direction. Therefore, an area of the electrode can be increased without increasing a distance between the electrodes. Consequently, capacitance between the electrodes detected by the detection circuit is increased, and the influence of noise is reduced.

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 ethanol concentration in the fuel is known. The ethanol 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 and the fuel injection timing according to the ethanol concentration. Thereby, while improving drivability, deterioration of exhaust gas is suppressed.
The fuel sensor described in Patent Document 1 includes an outer electrode ("side electrode 4" in Patent Document 1) and an inner electrode ("center electrode 5" in Patent Document 1) provided in the fuel passage. . The inner electrode is provided at a predetermined distance from the outer electrode on the radially inner side of the outer electrode formed in a cylindrical shape. The fuel sensor detects the ethanol concentration of the fuel from the change in the capacitance between the electrodes using the fuel as a dielectric (hereinafter the same applies to the “outer electrode and inner electrode”).

Japanese Utility Model Publication No. 1-163862

By the way, the fuel sensor is required to be small in size from the viewpoint of mounting property on a vehicle and manufacturing cost. In the fuel sensor described in Patent Document 1, when the area of the outer electrode and the inner electrode is reduced as the size of the body is reduced, the capacitance between the electrodes is reduced, and the dynamic range of the output signal is reduced. The effect of noise is increased. As a result, there is a concern that the detection accuracy deteriorates.
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.

According to the first aspect of the present invention, the fuel sensor is provided with the cylindrical outer electrode in the fuel passage through which the fuel flows. An inner electrode is provided on the radially inner side of the outer electrode with a predetermined distance from the outer electrode. The detection means detects an electrical characteristic of the fuel flowing through the inner flow path formed between the outer electrode and the inner electrode.
The inner electrode has a convex portion that protrudes from the outer wall in the radially outward direction toward the outer electrode. The outer electrode is located on the radially outer side of the convex portion and has a concave portion that is recessed radially outward from the inner wall of the outer electrode.

In general, the capacitance of a parallel plate capacitor can be obtained from Equation 1 below.
C = ε · (S / d) Equation 1
Where C is the capacitance (F) of the capacitor, ε is the dielectric constant (F / m), S is the electrode area (m ² ), and d is the distance (m) between the electrodes.
According to Equation 1, the capacitance is proportional to the area of the electrodes and inversely proportional to the distance between the electrodes.
In the invention which concerns on Claim 1, an electrode area becomes large by providing a convex part in an inner side electrode and providing a recessed part in an outer side electrode. Further, by providing the concave portion at a position radially outside the convex portion of the inner electrode, it is possible to prevent the distance between the electrodes from increasing. As a result, the capacitance between the electrodes using the fuel in the inner flow path as a dielectric increases, and the dynamic range of the output signal increases. Therefore, the influence of noise is reduced, and the detection accuracy of the fuel sensor can be increased.

According to the second aspect of the present invention, the convex portion of the inner electrode and the concave portion of the outer electrode are a certain distance at which the capacitance between the outer electrode and inner electrode can be detected using the fuel flowing through the inner flow path as a dielectric. Opened and provided.
This prevents an increase in the distance between the convex portion of the inner electrode and the concave portion of the outer electrode, thereby increasing the detection accuracy of the fuel sensor.

According to the invention of claim 3, the convex portion of the inner electrode and the concave portion of the outer electrode extend in the fuel flow direction of the inner flow path.
Thereby, the fluid resistance of the inner flow path is reduced. Therefore, the responsiveness of the fuel sensor with respect to a change in fuel properties can be enhanced.

According to a fourth aspect of the invention, the outer electrode is provided with a central axis substantially perpendicular to the flow direction of the fuel flowing through the fuel passage, and is located upstream and downstream in the flow direction of the fuel flowing through the fuel passage. At least two flow holes are provided. The concave portion of the outer electrode extends in the circumferential direction of the outer electrode. The convex part of the inner electrode extends in the circumferential direction of the inner electrode.
As a result, the central axis of the outer electrode is provided perpendicular to the fuel flow direction of the fuel passage, and the fluid resistance of the inner passage can be reduced. Therefore, the responsiveness of the fuel sensor with respect to a change in fuel properties can be enhanced.

According to the invention which concerns on Claim 5, the recessed part of an outer side electrode is extended helically to the inner wall of the radial direction inside of an outer electrode. The convex part of the inner electrode extends in a spiral manner on the outer wall of the inner electrode in the radial direction with the same lead angle as the concave part of the outer electrode.
As a result, it is possible to provide the inner electrode convex portion so as to fit inside the concave portion of the outer electrode, so that the outer diameter of the convex portion of the inner electrode is made larger than the inner diameter of the outer electrode. The distance between them can be reduced. For this reason, the electrostatic capacitance between electrodes becomes large and the dynamic range of an output signal becomes large. Therefore, the influence of noise is reduced, and the detection accuracy of the fuel sensor can be increased. The same lead angle means that when the convex part of the inner electrode fits inside the concave part of the outer electrode, the lead angle is such that a gap can be formed between the concave part of the outer electrode and the convex part of the inner electrode. Are the same.

According to the invention which concerns on Claim 6, an outer side electrode and an inner side electrode are assembled | attached by relative rotation.
Accordingly, the outer electrode and the inner electrode can be easily assembled by rotating relative to each other like a screw.

It is sectional drawing of the fuel sensor by 1st Embodiment of this invention. (A) is principal part sectional drawing of the fuel sensor by 1st Embodiment of this invention. (B) is the IIB-IIB sectional view taken on the line of FIG. 2 (A). (A) is principal part sectional drawing of the fuel sensor by 2nd Embodiment of this invention. (B) is the IIIB-IIIB sectional view taken on the line of FIG. 3 (A). (A) is principal part sectional drawing of the fuel sensor by 3rd Embodiment of this invention. (B) is the IVB-IVB sectional view taken on the line of FIG. 4 (A). (A) is principal part sectional drawing of the fuel sensor by 4th Embodiment of this invention. (B) is the VB-VB sectional view taken on the line of FIG. (A) is principal part sectional drawing of the fuel sensor by 5th Embodiment of this invention. (B) is the VIB-VIB sectional view taken on the line of FIG. 6 (A).

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 of this embodiment is a sensor that is provided in a fuel supply system that connects a fuel tank of a vehicle and a fuel injection device, and detects the concentration of ethanol contained in the fuel. The ethanol concentration detected by the fuel sensor 1 is transmitted to the ECU of the internal combustion engine. The ECU controls the fuel injection amount, fuel injection timing, ignition timing, and the like according to the ethanol 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 can be reduced.

As shown in FIG. 1, the fuel sensor 1 includes a fuel case 10, an outer electrode 30, an inner electrode 40, a thermistor 50 as a temperature sensor, a detection circuit 60 as a detection means, and the like.
The fuel case 10 is formed in a bottomed cylindrical shape from a metal such as stainless steel, for example, and forms a fuel passage 100 inside.
A supply pipe 11 is connected to one outer wall in the radial direction of the fuel case 10, and a discharge pipe 12 is connected to the other outer wall. The supply pipe 11 and the discharge pipe 12 are formed in a cylindrical shape from a metal such as stainless steel, and are fixed to the outer wall of the fuel case 10 by welding or the like. The fuel case 10 is provided with a supply opening 13 where the supply pipe 11 is connected, and with a discharge opening 14 where the discharge pipe 12 is connected.
A lid member 15 closes the opening opposite to the bottom of the fuel case 10.
The fuel flowing from the supply pipe 11 through the supply opening 13 and flowing into the fuel passage 100 inside the fuel case 10 flows through the fuel passage 100 and is discharged from the discharge opening 14 through the discharge pipe 12.

The outer electrode 30 is formed in a cylindrical shape from a metal such as stainless steel and is provided in the fuel passage 100 of the fuel case 10. The outer electrode 30 has an annular flange 31 extending radially outward from one of the axial directions, a thick portion 32 below the flange 31, and an electrode body 33 below the thick portion 32.
The flange 31 is locked to the lid member 15. The thick part 32 protrudes from the flange 31 to the fuel passage 100.
As shown in FIG. 2, the outer electrode 30 includes a first flow hole 36 positioned on the upstream side in the flow direction of the fuel flowing through the fuel passage 100 through the inner wall and outer wall in the radial direction of the electrode body 33, and the flow direction of the fuel It has the 2nd circulation hole 37 located in the downstream. The first flow hole 36 and the second flow hole 37 are formed in a U shape that opens to the bottom side of the fuel case 10.
The outer electrode 30 has a recess 34 that is recessed radially outward from the inner wall thereof. The recess 34 extends annularly in the circumferential direction of the outer electrode 30, and a plurality of recesses 34 are provided in the axial direction.

The inner electrode 40 is formed in a bottomed cylindrical shape from a metal such as stainless steel, for example, and is provided substantially coaxially with the outer electrode 30 on the radially inner side of the outer electrode 30. The outer diameter D1 of the inner electrode 40 is formed smaller than the inner diameter D2 of the outer electrode 30, and the inner electrode 40 is provided at a predetermined distance α from the outer electrode 30. For this reason, it is possible to insert the inner electrode 40 inside the outer electrode 30 from the axial direction and assemble the outer electrode 30 and the inner electrode 40. An inner flow path 41 through which fuel flows is formed between the inner electrode 40 and the outer electrode 30.
The inner electrode 40 has a convex portion 44 that projects radially outward from its outer wall. The convex portion 44 extends annularly in the circumferential direction of the inner electrode 40, and a plurality of convex portions 44 are provided in the axial direction.
The concave portion 34 of the outer electrode 30 and the convex portion 44 of the inner electrode 40 are provided so as to face each other in the radial direction. That is, the concave portion 34 of the outer electrode 30 is provided at a radially outer position of the convex portion 44 of the inner electrode 40. The convex portion 44 of the inner electrode 40 protrudes from the outer wall of the inner electrode 40 toward the concave portion 34 of the outer electrode 30.
The convex portion 44 of the inner electrode 40 and the concave portion 34 of the outer electrode 30 are provided with a certain distance β that can detect the capacitance between the electrodes using the fuel in the inner flow path 41 as a dielectric. Yes.
An insulator 42 made of glass is provided between the thick portion 32 of the outer electrode 30 and the inner electrode 40. The insulator 42 hermetically fixes the inner electrode 40 and the outer electrode 30 and electrically insulates the inner electrode 40 and the outer electrode 30 from each other.
The insulator 42 may be formed by an O-ring made of resin.

  As shown in FIG. 1, a thermistor 50 is provided inside the inner electrode 40. Terminals 51 and 52 of the thermistor 50 are supported by a support member 53 made of resin. The temperature of the fuel flowing through the inner flow path 41 is transferred to the thermistor 50 through the inner electrode 40. The thermistor 50 changes the electrical resistance as the temperature changes. The thermistor 50 can detect the temperature of the fuel flowing through the inner flow path 41.

An annular elastic member 16 is provided on the upper side of the lid member 15. A circuit case 61 is formed on the elastic member 16. The elastic member 16 prevents fuel from leaking between the lid member 15 and the circuit case 61.
The circuit case 61 is made of, for example, resin and includes a circuit board 62 on the inner side. The circuit board 62 is provided with a detection circuit 60 that detects the electrical characteristics of the fuel flowing through the inner flow path 41. A terminal 38 connected to the outer electrode 30, a terminal 43 connected to the inner electrode 40, and terminals 51 and 52 of the thermistor 50 are connected to the detection circuit 60.

The detection circuit 60 detects the electrostatic capacitance between the electrodes by charging / discharging between the outer electrode 30 and the inner electrode 40. The capacitance value varies depending on the dielectric constant of the fuel. The dielectric constant varies depending on the mixing ratio of gasoline and ethanol in the fuel and the fuel temperature. Therefore, the detection circuit 60 detects the ethanol concentration contained in the fuel flowing through the inner flow path 41 based on the capacitance between the electrodes and the fuel temperature detected by the thermistor 50.
A plate-shaped cover 63 covers the opening of the circuit case 61. The cover 63 prevents water or the like from entering the circuit case 61 from the outside.
A bracket 64 supports the outside of the fuel case 10. The bracket 64 is attached to the circuit case 61 with screws 65. Thereby, the fuel case 10 and the circuit case 61 are fixed.

This embodiment has the following effects.
(1) In this embodiment, the inner electrode 40 is provided with a convex portion 44, and the outer electrode 30 is provided with a concave portion 34. The convex portion 44 and the concave portion 34 are provided with a certain distance β capable of detecting the capacitance between the electrodes. Thereby, the electrode area can be increased without increasing the distance between the electrodes. For this reason, the capacitance between the electrodes detected by the detection circuit 60 increases, and the dynamic range of the output signal increases. Therefore, the fuel sensor 1 can reduce the influence of noise and increase the detection accuracy.
(2) In the present embodiment, the fuel that has flowed into the inner channel 41 from the first flow hole 36 of the outer electrode 30 passes through the inner channel 41 along the convex portion 44 of the inner electrode 40 and the concave portion 34 of the outer electrode 30. Flows out of the second flow hole 37 of the outer electrode 30. Since the convex portion 44 of the inner electrode 40 and the concave portion 34 of the outer electrode 30 extend in the fuel flow direction of the inner channel 41, the fluid resistance of the inner channel 41 is reduced. Therefore, the fuel sensor 1 can improve the responsiveness to changes in the properties of the fuel flowing through the fuel passage 100.

(Second Embodiment)
FIG. 3 shows a cross-sectional view of the main part of the fuel sensor according to the second embodiment of the present invention. 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 outer electrode 30 has a concave portion 341 extending spirally on the inner wall in the radial inner direction.
The inner electrode 40 has a convex portion 441 that spirally extends on the outer wall in the radially outward direction of the inner electrode 40 at a lead angle θ substantially the same as the concave portion 341 of the outer electrode 30. The concave portion 341 of the outer electrode 30 and the convex portion 441 of the inner electrode 40 are provided so as to face each other in the radial direction, and the convex portion 441 of the inner electrode 40 is fitted inside the concave portion 341 of the outer electrode 30.
The inner electrode 40 and the outer electrode 30 can be assembled by rotating relative to each other so that a male screw and a female screw are assembled. For this reason, the outer diameter D3 of the convex portion 441 of the inner electrode 40 is formed larger than the inner diameter D4 of the outer electrode 30. The convex portion 441 of the inner electrode 40 and the concave portion 341 of the outer electrode 30 are provided with a gap of a certain distance γ.

In the second embodiment, since the concave portion 341 of the outer electrode 30 and the convex portion 441 of the inner electrode 40 can be assembled like a screw, the distance γ between the electrodes is set to the distance β between the electrodes in the first embodiment. Can be made smaller. This increases the capacitance between the electrodes and increases the dynamic range of the output signal. Therefore, the fuel sensor can improve detection accuracy.
Also in the second embodiment, by setting the lead angle θ to be small, the convex portion 441 of the inner electrode 40 and the concave portion 341 of the outer electrode 30 can be brought closer to the fuel flow direction of the inner flow path 41. is there. Thereby, the fluid resistance of the inner flow path 41 is reduced, and the responsiveness of the fuel sensor to the change in the properties of the fuel flowing through the fuel passage 100 can be enhanced.

(Third embodiment)
FIG. 4 shows a cross-sectional view of a relevant part of a fuel sensor according to a third embodiment of the present invention. In the third embodiment, the concave portion 342 of the outer electrode 30 and the convex portion 442 of the inner electrode 40 both extend in the axial direction. The concave portion 342 of the outer electrode 30 and the convex portion 442 of the inner electrode 40 are provided so as to face each other in the radial direction, and the convex portion 442 of the inner electrode 40 is fitted inside the concave portion 342 of the outer electrode 30. The convex portion 442 of the inner electrode 40 and the concave portion 342 of the outer electrode 30 are provided with a gap of a certain distance η. The outer electrode 30 and the inner electrode 40 can be assembled by being inserted in the axial direction.

  Also in the third embodiment, the concave portion 342 of the outer electrode 30 is located radially outside the convex portion 442 of the inner electrode 40, and the convex portion 442 and the concave portion 342 are provided with a certain distance η. The electrode area can be increased and the distance between the electrodes can be decreased. This increases the capacitance between the electrodes and increases the dynamic range of the output signal. Therefore, the fuel sensor can improve detection accuracy.

(Fourth and fifth embodiments)
The fourth and fifth embodiments of the present invention are modifications of the first embodiment or the second embodiment.
In the fuel sensor according to the fourth embodiment, as shown in FIG. 5, the concave portion 343 of the outer electrode 30 and the convex portion 443 of the inner electrode 40 are formed like a round screw having a substantially semicircular cross section of the thread. ing.
In the fuel sensor according to the fifth embodiment, as shown in FIG. 6, the concave portion 344 of the outer electrode 30 and the convex portion 444 of the inner electrode 40 are formed like square screws with a vertical cross section of the thread. .
In addition, you may form the recessed part of the outer side electrode 30, and the convex part of the inner side electrode 40 like a trapezoid screw, a sawtooth screw, and a triangular screw, for example.
In the fourth and fifth embodiments, the same operational effects as those of the first to third embodiments described above can be achieved.

(Other embodiments)
In the plurality of embodiments described above, the sensor that detects the ethanol concentration contained in the fuel from the electrical characteristics between the electrodes has been described as the fuel sensor. On the other hand, this invention is good also as a sensor which detects the oxidation deterioration state of a fuel, etc. from the electrical property between electrodes.
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 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 30 ... Outer electrode 34, 341-344 ... Recess 36 ... 1st flow hole (flow hole)
37 ・ ・ ・ Second flow hole (flow hole)
40 ... inner electrode 41 ... inner flow paths 44, 441 to 444 ... convex portion 60 ... detection circuit (detection means)
100: Fuel passage

Claims (6)

A cylindrical outer electrode provided in a fuel passage through which fuel flows;
An inner electrode provided on the radially inner side of the outer electrode with a predetermined distance from the outer electrode;
Detecting means for detecting electrical characteristics of fuel flowing in an inner flow path formed between the outer electrode and the inner electrode;
The inner electrode has a convex portion protruding from the outer wall in the radially outward direction toward the outer electrode,
The fuel sensor according to claim 1, wherein the outer electrode has a concave portion that is located radially outside the convex portion and is recessed radially outward from an inner wall of the outer electrode.   The convex portion of the inner electrode and the concave portion of the outer electrode are spaced apart from each other by a certain distance capable of detecting a capacitance between the outer electrode and the inner electrode using the fuel flowing through the inner flow path as a dielectric. The fuel sensor according to claim 1, wherein the fuel sensor is provided.   The fuel sensor according to claim 1, wherein the convex portion of the inner electrode and the concave portion of the outer electrode extend in a fuel flow direction of the inner flow path. The outer electrode has a central axis substantially perpendicular to the flow direction of the fuel flowing through the fuel passage, and has at least two flow holes located upstream and downstream in the flow direction of the fuel flowing through the fuel passage. Have
The concave portion of the outer electrode extends in a circumferential direction of the outer electrode,
The fuel sensor according to claim 1, wherein the convex portion of the inner electrode extends in a circumferential direction of the inner electrode. The concave portion of the outer electrode extends spirally to the inner wall in the radial direction of the outer electrode,
The convex portion of the inner electrode extends in a spiral shape on the outer wall in the radially outward direction of the inner electrode at the same lead angle as the concave portion of the outer electrode. The fuel sensor according to item.   The fuel sensor according to claim 5, wherein the outer electrode and the inner electrode are assembled by relative rotation.

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