Fuel property sensor

In a fuel property sensor, a pair of first and second electrodes is arranged in a fuel chamber to measure an electric capacitance, thereby detecting a mixing ratio of alcohol to gasoline in a fuel of the fuel chamber. An outer wall surface of the first electrode is exposed in the fuel, and a sensing portion contacts an inner wall surface of the first electrode to detect a temperature of the fluid via the first electrode. One end portion of a lead is connected to the sensing portion and the other end portion thereof is connected to a plate portion attached to a housing. Furthermore, an elastic deformation portion is provided as a part of the lead to be elastically deformed, and to cause the sensing portion to be biased in a direction on which the sensing portion contacts the inner wall surface of the first electrode.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on Japanese Patent Application No, 2009-72608 filed on Mar. 24, 2009, the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a fuel property sensor which detects a fuel property of a vehicle, for example.

BACKGROUND OF THE INVENTION

Recently, alcohol-blended gasoline is used as fuel of vehicles in order to protect the environment. In this case, it is necessary to set an appropriate fuel injection amount and an ignition time based on a mixed ratio of the alcohol in the gasoline. Thus, in the vehicles, a sensor is generally provided so as to detect the mixed ratio of the alcohol to the gasoline. For example, in U.S. Pat. No. 7,030,629, an electrical characteristic of a fluid is measured so as to detect a fluid property, and the detected value is corrected based on a fluid temperature, thereby improving the detecting accuracy.

In the sensor described in U.S. Pat. No. 7,030,629, the electrical characteristic of the fluid to be detected is detected by using an electrode portion exposed to the fluid, and then the fluid property is determined based on the detected value and a fluid temperature measured by a temperature sensor via the electrode portion. The electrode portion and the temperature sensor are held inside of a housing exposed to the atmosphere. Therefore, heat is transmitted from the atmosphere via the housing, and thereby it is difficult to accurately measure the fuel temperature. When the fluid temperature cannot be accurately measured, the fluid property cannot be accurately detected.

In a fuel property sensor described in JP 1-163862U, an electrode portion is configured to have a hollow structure, and a temperature sensor is accommodated in the electrode portion. Thus, the temperature sensor can detect the temperature of the fuel without receiving heat from the atmosphere.

In the fuel property sensor described in JP 1-163862U, a sensing portion at a tip end of the temperature sensor is made to contact an inner wall of the electrode portion. Thus, if a dimension difference is caused in the electrode portion or the temperature sensor, it may difficult for the sensing portion to accurately contact the inner wall of the electrode portion, and thereby it may difficult to accurately measure the fuel temperature by using the temperature sensor. Furthermore, because the coefficient of linear expansion is generally different between the electrode portion and the temperature sensor, a stress may be applied to a conductive wire of the temperature sensor fixed to a substrate, and thereby the conductive wire of the temperature sensor may be damaged.

SUMMARY OF THE INVENTION

In view of the above points, it is an object of the present invention to provide a fuel property sensor, which can improve detection accuracy of a fuel temperature, thereby improving detection accuracy of a fuel property.

According to an aspect of the present invention, a fuel property sensor includes a housing defining a fuel chamber in which a fuel passes, a pair of first and second electrodes arranged in the fuel chamber to measure an electric capacitance therebetween so as to detect a mixing ratio of alcohol to gasoline in the fuel, a sensing portion contacting an inner wall surface of the first electrode, to detect a temperature of the liquid fluid via the first electrode, and a lead configured to support the sensing portion. In the fuel property sensor, the lead has one end portion connected to the sensing portion and the other end portion connected to a plate portion attached to the housing, and the first electrode is located such that an outer wall surface of the first electrode is exposed to the fuel. Furthermore, an elastic deformation portion is provided as a part of the lead, and is configured to be elastically deformed and to cause the sensing portion to be biased in a direction on which the sensing portion contacts the inner wall surface of the first electrode.

Thus, the sensing portion is pressed to the inner wall surface of the first electrode portion by using the elastic force (biasing force) of the elastic deformation portion, and thereby a contact state of the sensing portion to the inner wall surface of the first electrode can be accurately maintained. As a result, detection accuracy of the sensing portion for detecting the fluid temperature can be improved, thereby improving detection accuracy of a fuel property.

Furthermore, because the elastic deformation portion is provided as a part of the lead, it can prevent a breaking of the lead, even when a stress is applied to the lead due to a difference of the coefficient of liner expansion between the first electrode and the lead.

For example, a part of the lead may be bent to have a bent portion, and the elastic deformation portion may be configured by the bent portion. Furthermore/Alternatively, a holder fixed to the plate member may be disposed to be engaged with the inner wall surface of the first electrode. In this case, the holder has a receiving portion in which the elastic deformation portion is held to be electrically insulated from the first electrode. Furthermore, the holder may have therein a communication passage communicating with the receiving portion. In this case, the lead penetrates through the communication passage.

Furthermore/Alternatively, the first electrode may be provided with an approximately cylindrical wall portion with a bottom, to define therein an inner space partitioned from the fuel in the fuel chamber. In this case, the sensing portion is disposed in the inner space of the cylindrical wall portion of the first electrode to contact an inner surface of the cylindrical wall portion of the first electrode. In addition, the sensing portion may be disposed to contact the inner surface of the bottom of the cylindrical wall portion of the first electrode, and the lead may extend in the cylindrical wall portion of the first electrode from the sensing portion in an axial direction.

Furthermore/Alternatively, the second electrode may be located to opposite to the first electrode. For example, the second electrode may have an approximately cylindrical shape, and the first electrode may be disposed inside of the second electrode.

In the fuel property sensor, a circuit element portion may be configured to correct the measured electric capacitance based on the temperature detected by the sensing portion, so as to determine the mixing ratio of the alcohol to the gasoline.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present embodiment, the present invention is typically applied to a fuel property sensor which uses a fuel as a detection subject, in which an alcohol is mixed in gasoline. The fuel property sensor measures an electric capacitance in accordance a relative permittivity of the fuel as an electrical characteristic, and detects a mixing ratio of the alcohol to the gasoline as a fuel property.

First, a basic structure of a fuel property sensor1of the embodiment will be described with reference toFIGS. 1-4.

As shown inFIG. 1, the fuel property sensor1includes a first housing11, an electrode portion30, a second housing51and the like.

The first housing11is made of a metal such as stainless or a resin or the like, and is formed approximately into a one-side open cylindrical shape having a bottom. The first housing11is provided with a fuel chamber14therein, and fuel pipes12,13are bonded and fixed to side walls of the first housing11, respectively. A fuel passage17is provided in an inner portion of the fuel pipe12to communicate with a fuel opening15opened at one side wall of the first housing11, and a fuel passage18is provided in an inner portion of the fuel pipe13to communicate with a fuel opening16opened at another side wall of the first housing11.

The fuel pipes12,13are connected respectively to fuel pipes coupled to a fuel tank (not shown) or coupled to an injector (not shown). Thus, the fuel flowing in the fuel pipes12,13can flow into the fuel chamber14.

A bracket20is located to cover the bottom portion of the first housing11, as shown inFIGS. 1 and 3. The bracket20is provided with a plurality of flanges26,27,28,29, and holes are provided in the flanges26,27,28,29, respectively. The bracket20is screwed to a second housing51at the flanges26,27,28,29, so that the first housing11is assembled to the second housing51via the flanges26,27,28,29of the bracket20.

A cover member21is formed into an approximate circular shape by using a metal such as stainless. The cover member21is provided with a flange portion22, a first step portion23having a radial dimension of an open area smaller than that of the flange portion22, and a second step portion24having a radial dimension of an open area smaller than that of the first step portion23. An approximately circular receiving hole25is provided in the second step portion24. The cover member21is melted and fixed to a flange portion19provided at an open side of the first housing11.

The electrode portion30includes a pair of a first electrode31and a second electrode41. The first electrode31is made of a metal such as a stainless, for example, and is formed into an approximately cylindrical shape having a closed bottom. A thermistor60is accommodated in a cylindrical space of the first electrode31.

The second electrode41is made of a metal such as a stainless, and is formed into an approximately cylindrical shape having an open bottom. The second electrode41is located outside of the first electrode31. The second electrode41includes a small-diameter portion42, a middle-diameter portion43having a diameter larger than the small-diameter portion42, and a large-diameter portion44having a diameter larger than that of the middle-diameter portion43. A side wall of the small-diameter portion42is provided with cut portions45,46at two positions, each of which is formed into approximately a U-shape, as shown inFIG. 4. A clearance between the first electrode31and the large-diameter portion44of the second electrode41is air-tightly sealed by a glass member35.

The electrode portion30including the pair of the first and second electrodes31,41is located in the receiving hole25of the cover member21inside of the housing11, to be engaged with the receiving hole25of the cover member21. More specifically, the middle-diameter portion43and the small-diameter portion42of the second electrode41are arranged inside of the receiving hole25, and an outer step portion between the middle-diameter portion43and the larger-diameter portion44is engaged with the cover member21at a side of the receiving hole25. Thus, an opening portion of the first housing11is liquid-tightly sealed by the cover member21and the electrode portion30. The first electrode31, and the small-diameter portion42and the middle-diameter portion of the second electrode41are exposed in the fuel within the fuel chamber14, and are adapted to measure the electrical characteristics of the fuel.

The second housing51is arranged adjacent to the cover member21of the first housing11, as shown inFIG. 1. As shown inFIG. 3, the second housing51is formed approximately into a one-side opened cylindrical shape having a bottom. The second housing51is made of a resin or the like, and is formed into approximately a one-side opened cylindrical shape. A substrate53is located in the second housing51, as shown inFIG. 1. The substrate53is provided with a circuit element portion54in which a conversion circuit for converting between the electric capacitance (C) and the voltage (V), or a sampling circuit, or the like is provided.

The thermistor60is electrically connected to the substrate53, as a part of the circuit element portion54. A first conductive wire32electrically connected to the first electrode31, and a second conductive wire47electrically connected to the second electrode41are electrically connected to the substrate53, respectively, as a part of the circuit element portion54. The substrate53is electrically connected to a terminal (not shown) of a connector55located at a side surface of the second housing51, and the connector55is connected to an ECU by using a wire (not shown).

An approximately circular receiving hole52is provided in a bottom portion of the second housing51. An elastic member57has therein an approximately circular hole58that has a radial dimension approximately equal to the radial dimension of the receiving hole52. The elastic member57is attached to a bottom surface of the second housing51, and is inserted between the cover member21and the bottom surface of the second housing51to contact the bottom surface of the second housing51and the first step portion23of the cover member21. The elastic member57is made of an insulation material such as an elastomer, for example, and is formed into approximately a circular shape. The elastic member57is located to prevent a heat transmission from the substrate53toward the inside of the first housing11. An opening of the second housing51is tightly covered by a cover59.

The thermistor60is located inside of the first electrode31. The thermistor60includes a sensing portion61and a lead62. The thermistor60is adapted as a part of the circuit element portion54, and the lead62is electrically connected to the substrate53by soldering, for example, at a side opposite to the sensing portion61. Therefore, the lead62can support the sensing portion61. The sensing portion61is arranged to contact an inner bottom surface33of the cylindrical first electrode31. Thus, a fuel temperature in the fuel chamber14is transmitted to the sensing portion61via the first electrode31, so that the fuel temperature in the fuel chamber14can be measured by the sensing portion61.

When a voltage is applied between the first electrode31and the second electrode41, the first electrode31and the second electrode41are adapted as electrodes of a condenser using the fuel in the fuel chamber14as a dielectric material.

A relative permittivity of the fuel in the fuel chamber14is changed based on a mixing ratio of ethanol to gasoline. For example, in a case where the relative permittivity of the gasoline is about 2 and the relative permittivity of ethanol is about 25, the relative permittivity of the ethanol blended fuel is changed approximately in a range between 2 to 25, in accordance with the mixing ratio of the ethanol to the gasoline. The electric capacitance is a value corresponding to the relative permittivity. Thus, by measuring the electric capacitance between the first electrode31and the second electrode41, the mixing ratio of the ethanol to the gasoline can be determined.

The electric capacitance is changed based on the fuel temperature at the measuring time. In the present embodiment, a measured value of the electric capacitance between the first electrode31and the second electrode41is corrected in the circuit element portion54based on the fuel temperature detected by the thermistor60, and then the mixing ratio of the ethanol to the gasoline is determined based on the corrected electric capacitance in the circuit element portion54. Thereafter, the determined result is transmitted to the ECU.

Because the detected value of the mixing ratio of the ethanol to the gasoline is corrected based on the fuel temperature, the ECU can accurately set an appropriate fuel injection amount and an ignition timing based on the determined value.

Next, the structure of the fuel property sensor1of the present embodiment will be described in detail. As shown inFIG. 1, an elastic deformation portion63is provided as a part of the lead62of the thermistor60, in the fuel property sensor1. In the example ofFIG. 1, a part of the lead62is bent to have a bent portion so as to configure the elastic deformation portion63. The elastic deformation portion63is provided in the lead62to cause the sensing portion61to be biased in a direction so that the sensing portion61tightly contacts the bottom inner surface33of the cylindrical first electrode31by using the biasing force of the elastic deformation portion63. The lead62is assembled and connected to the substrate53in a constriction state of the elastic deformation portion63.

A holder65is provided to hold the thermistor60. One end of the holder65is fixed to the substrate53, and the thermistor60is held by the holder65to be engaged with the holder65. The holder65is made of a resin, and two parts of the elastic deformation portion63are accommodated in two receiving portions66,67of the holder65, respectively. Therefore, the elastic deformation portion63of the lead62can be electrically insulated by the holder65, so as to prevent the elastic deformation portion63from directly contacting the inner wall surface34of the first electrode31.

The holder65is provided with two communication passages68,69communicating with the two receiving portions66,67, respectively. Thus, two wire parts of the lead62including the elastic deformation portion63are electrically insulated by the holder65, respectively. The communication passages68,69are provided in the holder65such that a diameter of each communication passage68,69is slightly larger than a wire diameter of the two part of the lead62. Thus, the position of the lead62is set when the lead62passes through the communication passages68,69, and thereby the lead53can be accurately assembled to the substrate53at a predetermined position.

Thus, by the biasing force (elastic force) of the elastic deformation portion63, the sensing portion61is pressed to the bottom inner surface33of the cylindrical first electrode31, thereby keeping a contact state at which the sensing portion61tightly contacts the bottom inner surface33of the cylindrical first electrode31. Therefore, it can prevent the sensing portion61from being separated from the bottom inner surface33of the cylindrical first electrode31, thereby improving a detection accuracy of the fuel temperature in the sensing portion61. As a result, a detection accuracy in the fuel property of the fuel property sensor can be improved.

In the fuel property sensor1of the present embodiment, even when the coefficient of liner expansion is different between the first electrode31and the lead62so as to apply a stress to the lead62, it can prevent breaking of the lead62.

Furthermore, because a part of the lead62is bent to configure the elastic deformation portion63by using the bent portion, the elastic deformation portion63can be easily formed as compared with a case where the elastic deformation portion63is a member formed separated from the lead62.

In the fuel property sensor1of the present embodiment, because the two parts of the elastic deformation portion63are received respectively in the receiving portions66,67of the holder65to be elastically insulated from the first electrode31, it can prevent the elastic deformation portion63from contacting the first electrode31.

Because the position of the lead62can be determined while the wires of the lead62pass through the communication passage68,69of the holder65, the assembling performance of the thermistor60to the substrate53can be improved.

In the fuel property sensor1of the present embodiment, the first electrode31has approximately a cylindrical shape having a bottom, the sensing portion61is arranged to contact the bottom inner surface33, and the fuel temperature flowing in the fuel chamber14is detected via the first electrode31. Because the first electrode31can be immersed in the liquid fuel, the fuel temperature can be accurately detected via the first electrode31. Thus, even when the size of the first electrode31is made small, an exposed area of the first electrode31in the liquid fuel can be secured, thereby reducing the size of the electrode portion30.

In the fuel property sensor1of the present embodiment, the second electrode41is formed into approximately a cylindrical shape, and the first electrode31having the bottom is located inside of the second electrode41to be exposed to the liquid fuel from a bottom side of the second electrode41.

The present invention is not limited to the above embodiment.

For example, according to an aspect of the present embodiment, a fuel property sensor (1) includes a housing defining a fuel chamber (14) in which a liquid fuel passes, a pair of first and second electrodes (31,41) arranged in the fuel chamber (14) to measure an electric capacitance therebetween so as to detect a mixing ratio of alcohol to gasoline in the liquid fuel, a sensing portion (61) contacting an inner wall surface of the first electrode (31) to detect a temperature of the liquid fluid via the first electrode (31), and a lead (62) configured to support the sensing portion (61). The first electrode (31) is located such that an outer wall surface of the first electrode (31) is exposed in the liquid fuel, and the lead (62) has one end portion connected to the sensing portion (61) and the other end portion connected to a plate portion (53) attached to the housing. Furthermore, an elastic deformation portion (63) is provided as a part of the lead (62), and is configured to be elastically deformed and to cause the sensing portion (61) to be biased in a direction on which the sensing portion (61) contacts the inner wall surface of the first electrode (31).

In the above embodiment, the other portions of the fuel property sensor may be suitably modified.

The present invention is not limited to the above-described embodiment, and can be modified in various ways without departing from the scope of the invention.

For example, in the above-described embodiment, the present invention is typically applied to a fuel property sensor of an electric capacitance type, which measures an electric capacitance of a liquid fluid to be detected (e.g., a liquid fuel) by using a pair of the first electrode31and the second electrode41opposite to each other, and detects the fuel property based on the measured electric capacitance. However, the present invention may be applied to a fuel property sensor which measures an impedance of the liquid fuel to be detected, and determines a fuel property of the liquid fuel based on the detected impedance. In an electrode portion for detecting the impedance, the first and second electrodes as the electrode portion are unnecessary to be opposite to each other if the electrode portion is exposed in the liquid fuel directly.