JP4254457B2 - Vehicle level detection device - Google Patents

Description

  The present invention relates to a vehicular liquid level detection device that is mounted on a vehicle and detects a liquid level position of the liquid, and is suitable for use in detecting a fuel liquid level in a fuel tank installed in an automobile, for example. is there.

  2. Description of the Related Art Conventionally, in a vehicle such as an automobile, there is a vehicle liquid level detection device that detects a fuel liquid level as means for detecting the amount of liquid stored in a tank, for example, the amount of fuel. This is because a floating arm is provided on the float that floats on the surface of the fuel, the rotating arm is rotated in accordance with the change in the position of the float due to the fluctuation of the liquid level, and the change in the rotation angle is converted into, for example, a change in electrical resistance. Is common. However, such a mechanical liquid level detection device has problems such as a large physique and a limited installation location, or poor detection accuracy.

  In order to solve such a problem, instead of mechanically detecting the liquid level, for example, a method of detecting the liquid level by emitting an ultrasonic wave and receiving a reflected wave from the liquid level, that is, a non-contact type Detection methods have been proposed.

  For example, an ultrasonic sensor including an ultrasonic oscillation element and a cylinder is disposed at one end opening of a cylinder disposed at the bottom of the liquid container, and an ultrasonic oscillation is performed at the other end of the cylinder. There is a configuration in which a reflector that reflects ultrasonic waves emitted from an element toward a liquid surface through an opening provided in a cylindrical body is disposed (for example, see Patent Document 1).

  In such a liquid level detection device, the time from when the ultrasonic oscillation element emits the ultrasonic wave until the ultrasonic oscillation element receives the reflected wave of the ultrasonic wave at the liquid level, that is, the ultrasonic wave is The time required to reciprocate between the acoustic wave oscillating element and the liquid surface is measured, and the liquid surface position is detected based on the measured time.

Thereby, the physique of a liquid level detection apparatus can be reduced in size, and detection accuracy can be improved.
JP 11-153471 A

  In the above-described conventional liquid level detection device, the cylinder has a square cross section, and the ultrasonic oscillation element is coaxially disposed on the cylinder.

  Further, since the cylindrical body is attached to the tank bottom portion with the axial direction parallel to the liquid surface, the central axial direction of the ultrasonic oscillation element is also parallel to the liquid surface. In addition, the reflector is 45 with respect to the liquid surface so that the path of the ultrasonic wave in the central axis direction of the ultrasonic oscillation element reflected by the reflector and traveling toward the liquid surface coincides with the path of the reflected wave from the liquid surface. ° It is formed as an inclined slope. Thereby, the ultrasonic wave traveling on the central axis of the ultrasonic oscillation element is reflected on the liquid surface and enters the ultrasonic oscillation element along the same path as the forward path.

  By the way, ultrasonic waves are emitted radially and conically from the ultrasonic oscillator. For this reason, a part of the ultrasonic wave emitted from the ultrasonic oscillation element, that is, an ultrasonic wave traveling in a direction deviating from the central axis direction of the ultrasonic oscillation element, is transmitted along the ultrasonic propagation path before reaching the reflector. It enters the wall of a cylinder and diffuses there. As described above, the propagation path length of the ultrasonic wave incident on the ultrasonic oscillation element through the reflector, the liquid surface, and the reflector while repeating irregular reflection on the wall of the cylindrical body is on the central axis of the ultrasonic oscillation element described above. It becomes longer than the propagation path of the traveling ultrasonic wave. For this reason, an error may occur in liquid level detection, that is, accurate liquid level detection may not be performed.

  Moreover, in the conventional liquid level detection apparatus, the cylinder has a square cross section. On the other hand, ultrasonic waves are emitted radially and conically from the ultrasonic oscillator. Since the ultrasonic wave radiated in a conical shape travels in the propagation path of the square cross section, ultrasonic interference occurs at the four corners of the cylindrical body, and the ultrasonic propagation energy decreases. As a result, the energy of the reflected wave from the liquid surface incident on the ultrasonic oscillating element is reduced, and the detection signal level emitted by the ultrasonic oscillating element is also lowered accordingly, which may prevent accurate liquid level detection. .

  Furthermore, in the conventional liquid level detection apparatus, the cylinder is provided between the ultrasonic oscillation element and the reflector, and is not provided between the reflector and the liquid level. For this reason, the ultrasonic wave reflected from the liquid surface is diffused in all directions in the tank, and the energy of the reflected wave re-entering the reflector is reduced. Therefore, the reflected wave from the liquid surface incident on the ultrasonic oscillation element is reduced. Energy may be reduced and accurate liquid level detection may not be performed.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a vehicle liquid level detection device capable of highly accurate liquid level detection by devising a configuration of a cylindrical body. is there.

  The present invention employs the following technical means to achieve the above object.

In the liquid level detecting device for a vehicle according to claim 1 of the present invention, a tank for storing liquid, an ultrasonic oscillation element arranged at the bottom of the tank, and an ultrasonic wave emitted by the ultrasonic oscillation element in the tank And a reflection member having a reflection surface that reflects toward the liquid surface of the liquid, and the reflected wave reflected by the liquid surface of the ultrasonic wave emitted from the ultrasonic oscillation element is received by the ultrasonic oscillation element through the reflection surface In the vehicular liquid level detection apparatus that detects the liquid level position, the first cylinder having a cylindrical shape that is an ultrasonic wave propagation path between the ultrasonic oscillation element and the reflection member, and the ultrasonic wave between the reflection member and the liquid level And a second cylinder having a cylindrical shape as a propagation path, the inner diameter of the first cylinder and the inner diameter of the second cylinder are substantially equal , and the inner diameter of the first cylinder and the inner diameter of the second cylinder are configured to be smaller than the diameter of the oscillation plane to fire ultrasonic It is.

  In this case, the first and second cylinders have a circular cross-sectional shape, thereby preventing a reduction in ultrasonic propagation energy due to ultrasonic interference at the four corners of the cylinder having a square cross section in the conventional liquid level detection device. As a result, the level of the detection signal emitted from the ultrasonic oscillation element due to the reflected wave from the liquid surface can be increased. As a result, it is possible to provide a vehicular liquid level detection device capable of highly accurate liquid level detection.

  Here, the propagation speed when the ultrasonic wave travels in the liquid filled in the circular pipe line is a function of the elastic coefficient of the circular pipe line and the radius of the circular pipe line. Therefore, if the radius of the circular pipe line changes as the ultrasonic wave travels in the liquid filled in the circular pipe line, the propagation speed of the ultrasonic wave changes accordingly. Arise.

In the liquid level detecting device for a vehicle according to claim 2 of the present invention, the first cylinder and the second cylinder are formed of the same material, and the inner diameters of the first cylinder and the second cylinder are formed to be equal to each other. Since the propagation speed of the ultrasonic wave in the liquid in the inside and the propagation speed of the ultrasonic wave in the liquid in the second cylinder can be made substantially equal, the propagation energy loss of the ultrasonic wave at the transition between the first cylinder and the second cylinder can be reduced. It is possible to provide a vehicular liquid level detection device capable of suppressing liquid level detection with high accuracy.

In the liquid level detecting device for a vehicle according to claim 3 of the present invention, the wall thickness of the first cylinder and the wall thickness of the second cylinder are formed to be substantially equal.

  Thereby, since the propagation speed of the ultrasonic wave in the liquid in the first cylinder and the propagation speed of the ultrasonic wave in the liquid in the second cylinder can be made equal, the ultrasonic wave at the time of transition between the first cylinder and the second cylinder Therefore, it is possible to provide a vehicular liquid level detection device capable of highly accurately detecting the liquid level by reliably suppressing the propagation energy loss and increasing the detection signal level generated by the ultrasonic oscillation element by the reflected wave from the liquid level.

  When the ultrasonic wave propagates in the liquid, ultrasonic energy loss occurs when the ultrasonic wave propagation speed changes due to some cause, for example, a change in the shape and material of a pipe line through which the ultrasonic wave propagates. For this reason, in the vehicle liquid level detection device, the detection signal level emitted from the ultrasonic oscillation element is lowered by the reflected wave from the liquid level, and it may be difficult to detect the liquid level with high accuracy.

In this case, the configuration of the liquid level detecting device for a vehicle according to claim 4 of the present invention, that is, the first cylinder and the second cylinder are formed of different materials, and the inner diameter of the first cylinder and the inner diameter of the second cylinder. And the wall thickness of the first cylinder and the wall thickness of the second cylinder are set so that the speed of sound in the liquid in the first cylinder and the speed of sound in the liquid in the second cylinder are equal. The ultrasonic wave propagation energy loss at the time of transition between one cylinder and the second cylinder is surely suppressed, and the detection signal level generated by the ultrasonic oscillation element by the reflected wave from the liquid surface is increased, thereby enabling highly accurate liquid surface detection. A liquid level detecting device for a vehicle can be provided.

  Further, the second cylinder is formed as a material different from the first cylinder, that is, as a separate part. Accordingly, when manufacturing a plurality of types of vehicle liquid level detection devices corresponding to a plurality of types of tanks having different liquid level heights during maximum liquid storage, the ultrasonic oscillation element, the first cylinder and the reflecting member are common specifications. And an easy method of setting a plurality of types of the second cylinder, which is an ultrasonic wave propagation path from the reflecting surface to the liquid surface, is possible, and a plurality of types of vehicle liquids are provided with a minimum cost increase. A surface detection device can be manufactured.

In the vehicle level detecting apparatus according to claim 1 of the present invention, the inner diameter and the inner diameter of the second cylinder of the first cylinder is smaller than the diameter of the oscillation plane to fire ultrasonic ultrasonic oscillation device configuration It is said.

  When the ultrasonic wave is emitted into the first cylinder having a diameter larger than the oscillation surface diameter of the ultrasonic oscillation element, that is, when the distance from the outer edge of the oscillation surface to the inner wall of the first cylinder is large, the ultrasonic wave reaches the inner wall. As a result, the detection signal level generated by the ultrasonic oscillating element is lowered by the reflected wave from the liquid surface.

Therefore, with the configuration such as a vehicle for liquid level detecting apparatus according to claim 1 of the present invention, by suppressing the attenuation of the ultrasound energy emitted from the oscillation plane, the reflected wave from the liquid surface Ultra It is possible to provide a vehicular liquid level detection device capable of increasing the detection signal level generated by the sound wave oscillating element and capable of detecting the liquid level with high accuracy.

  Hereinafter, an example in which a vehicle liquid level detection device according to an embodiment of the present invention is applied to a fuel liquid level detection device 1 for detecting a fuel liquid level position in a fuel tank of an automobile will be described with reference to the drawings. To do.

  FIG. 1 is a partial cross-sectional view of a fuel tank 2 that is a tank for storing fuel 8 as a liquid in a fuel level detecting device 1 according to an embodiment of the present invention. In FIG. 1, the vertical direction in the figure is the vertical direction of the automobile. Further, a liquid level 81 in FIG. 1 indicates a liquid level position when the amount of fuel 8 stored in the fuel tank 2 is maximum, that is, when the fuel tank 2 is full.

  FIG. 2 is a schematic diagram for explaining an electric circuit configuration in the fuel level detecting device 1 according to the embodiment of the present invention.

  As shown in FIG. 1, the fuel level detection device 1 is integrally formed with a fuel tank 2 that is a tank, an ultrasonic element 3 that is an ultrasonic oscillation element, a guide pipe 4 that is a first cylinder, and a guide pipe 4. The reflecting plate 41 is a reflecting member and the guide pipe 5 is a second cylinder. That is, as shown in FIG. 1, the guide pipe 4 is attached to the bottom surface 21 of the fuel tank 2.

  Below, the structure of the fuel liquid level detection apparatus 1 is demonstrated.

  As shown in FIG. 1, the ultrasonic element 3 that is an ultrasonic oscillation element is fixed to one end of a guide pipe 4 to be described later via a bracket 6. That is, as shown in FIG. 1, an oscillation surface for emitting ultrasonic waves is fixed to face the guide pipe 4.

  The ultrasonic element 3 is made of a material having a piezo effect (a characteristic that changes in volume when a voltage is applied, and generates a voltage when receiving an external force), such as PZT (lead zirconate titanate). Yes. As shown in FIG. 1, the ultrasonic element 3 includes a lead wire 7 for connecting to an external electric circuit. The lead wire 7 extends outside the bracket 6 and is airtight outside the fuel tank 2. Has been drawn to. That is, when a pulse voltage is applied to the ultrasonic element 3 through the lead wire 7, the oscillation surface 31 vibrates, and thereby ultrasonic waves are emitted from the oscillation surface 31 into the fuel 8. On the other hand, when the reflected wave reflected by the liquid surface reaches the oscillating surface 31 and the oscillating surface 31 vibrates due to the pressure action, the ultrasonic element 3 generates a voltage, which causes the lead wire 7 as an output signal. Output to the outside. The oscillation surface 31 of the ultrasonic element 3 is formed in a circular shape.

  The bracket 6 is made of resin or metal, and holds and fixes the ultrasonic element 3. Further, as shown in FIG. 1, the bracket 6 is arranged on one end side (right side in FIG. 1) of the guide pipe 4 with the oscillation surface of the ultrasonic element 3 facing the other end of the guide pipe 4, that is, the ultrasonic element. The ultrasonic wave emitted by 3 is fixed so as to propagate toward the other end side of the guide pipe 4.

The guide pipe 4 is made of, for example, a resin material or a metal material. In the fuel level detecting device 1 according to one embodiment of the present invention, the guide pipe 4 is formed of an aluminum die casting alloy. The ultrasonic element 3 is attached to one end side (right side in FIG. 1) of the guide pipe 4 via a bracket 6. In addition, a reflecting plate 41 as a reflecting member is disposed on the other end side (left side in FIG. 1) of the guide pipe 4. The reflection plate 41 is formed integrally with the guide pipe 4 from an alloy for aluminum die casting. The reflection plate 41 is provided with a reflection surface 42 that reflects the ultrasonic wave emitted from the ultrasonic element 3 toward the liquid surface 81 in the fuel tank 2. That is, the guide pipe 4 forms an ultrasonic propagation path between the ultrasonic element 3 and the reflection plate 41. The guide pipe 4 is formed in a cylindrical shape in cross section, and has an inner diameter d ₁ and a wall thickness t ₁ as shown in FIG. The inner diameter d ₁ of the guide pipe 4 is set smaller than the diameter D ₃ of the oscillation surface 31.

  As shown in FIG. 1, the reflection surface 42 directs the ultrasonic wave emitted from the ultrasonic element 3 and traveling along the propagation path A on the axis of the ultrasonic element 3 toward the liquid surface 81, and the incident angle to the liquid surface 81. Is set to reflect in the direction in which the angle becomes 0 °, that is, in the direction orthogonal to the liquid surface 81. That is, as shown in FIG. 1, the reflecting surface 42 is provided with an inclination of 45 ° with respect to the liquid surface. Thereby, the ultrasonic wave emitted from the oscillation surface 31 of the ultrasonic element 3 and traveling along the propagation path A on the axis of the ultrasonic element 3 is reflected by the reflecting surface 42, reaches the liquid surface 81, and is reflected by the liquid surface 81. Thereafter, the light enters the oscillation surface 31 along the same path as the forward path.

  As shown in FIG. 1, a guide pipe 5 as a second cylinder, which is an ultrasonic wave propagation path between the reflecting surface 42 and the liquid surface, is attached to the reflecting plate 41.

The guide pipe 5 is formed from a stainless steel circular tube with an inner diameter dimension d ₂ and a wall thickness t ₂ , and is fixed to the reflection plate 41 portion of the guide pipe 4 by, for example, press-fitting as shown in FIG. . As shown in FIG. 1, the total length L of the guide pipe 5 is such that the tip of the guide pipe 5 at the liquid level 81 side is the liquid level position when the amount of fuel 8 stored in the fuel tank 2 is maximum, that is, when the tank is full. The liquid level 81 is set so as to protrude upward by a length ΔL. In the fuel level detecting device 1 according to the embodiment of the present invention, the inner diameter d ₂ of the guide pipe 5 is set equal to the inner diameter d ₁ of the guide pipe 4.

Here, in the fuel level detecting device 1 according to the embodiment of the present invention, the thickness d ₁ of the guide pipe 4 and the thickness d ₂ of the guide pipe 5 are the sound velocity c in the fuel 8 in the guide pipe 4. ₁ and the speed of sound c ₂ in the fuel 8 in the guide pipe 5 are set to be equal.

Hereinafter, in an embodiment a fuel level detecting device according to one of the present invention will be described concept for setting the wall thickness d ₂ of the wall thickness d ₁ and the guide pipe 5 of the guide pipe 4.

  First, the speed of sound in the liquid in the tube filled with the liquid is obtained by the following equation (see Equation 1).

(Equation 1)
_{c 0 / c = (1 +} 2E 0 / E M * a / h) -1/2
In Equation 1, c ₀ is the liquid sound velocity in the tube, c is the liquid sound velocity, E ₀ is the bulk modulus of the liquid, E _M is the longitudinal elastic modulus of the tube wall material, a is the inner radius of the tube, and h is the tube wall thickness. It is.

  Using Equation 1, the sound speed of the fuel in the two guide pipes 4 and 5 in the fuel level detecting device 1 according to the embodiment of the present invention is expressed.

The fuel 8 sonic velocity in the guide pipe 4 is c ₁ , the longitudinal elastic modulus of the guide pipe 4 material is E _M1 , the fuel 8 sonic velocity in the guide pipe 5 is c ₂ , the longitudinal elastic modulus of the guide pipe 5 material is E _M2 , and the fuel 8. When the speed of sound and c _F, E _F the bulk modulus of the fuel 8, fuel 8 sound velocity c ₁ and the guide pipe c ₂ fuel 8 sound velocity in 5 of the guide pipe 4 is represented by the formula shown below, respectively (See Formulas 2 and 3).

(Equation 2)
_{c 1 / c F = (1} + 2E F / E M1 * d 1 / 2t 1) -1/2

(Equation 3)
c ₂ / c _F = (1 + 2E _F / EM ₂ * d ₂ / 2t ₂ ) ^−1/2
In Equation 2 and Equation _{3, c 1 = c 2,} d 1/2 = d 2/2, as, when guiding the relationship between the wall thickness _{t 2} of the wall thickness _{t 1} and the guide pipe 5 of the guide pipes 4 The following formula is obtained (see Formula 4).

(Equation 4)
t ₂ = t ₁ * E _M1 / E _M2
In the fuel level detecting device 1 according to one embodiment of the present invention, the guide pipe 4 is formed from an aluminum die casting alloy, and the guide pipe 5 is formed from a stainless steel pipe. Therefore, if E _M1 = 72 GPa and E _M2 = 204 GPa, t2 = t1 × 0.353. That is, the thickness t ₂ of the guide pipe 5 is set to 0.35 times the thickness t ₁ of the guide pipe 4, in other words, approximately 1/3 of the thickness t ₁ of the guide pipe 4. For example, the speed of sound c ₁ in the fuel 8 in the guide pipe 4 and the speed of sound c ₂ in the fuel 8 in the guide pipe 5 can be made equal.

  Next, an electric circuit configuration of the fuel level detecting device 1 according to the embodiment of the present invention will be described with reference to FIG.

  As shown in the electric circuit configuration diagram of FIG. 2, the control circuit 9 is connected to the battery 12 via the ignition switch 11. In addition, the ultrasonic element 3 is connected to the control circuit 9. The control circuit 9 is connected to the display unit 10.

  The control circuit 9 is composed of, for example, a microcomputer, and processes a reflected wave reception signal output from the pulse generation circuit 91 for applying a pulse voltage signal to the ultrasonic element 3 and the ultrasonic element 3, and based on it. An arithmetic circuit 92 for calculating the liquid level position, and a drive circuit 93 for outputting a drive signal for driving the display unit 10 based on the liquid level position signal calculated by the arithmetic circuit 92. When the ignition switch 11 is turned on and electric power is supplied from the battery 12, the control circuit 9 starts the operation of the fuel level detecting device 1.

  The display unit 10 includes, for example, a pointer instrument or a liquid crystal panel, and is installed in a combination meter (not shown) in front of the driver's seat of the automobile. The display unit 10 is driven by the drive circuit 93 of the control circuit 9 and displays the liquid level position calculated by the arithmetic circuit 92, that is, the remaining amount of fuel in the fuel tank so that the driver can visually recognize it.

  Next, the fuel level detection operation of the fuel level detection device 1 according to one embodiment of the present invention will be described.

  When a pulse voltage signal is applied to the ultrasonic element 3 by the pulse generation circuit 91, the oscillation surface 31 vibrates and pulsed ultrasonic waves are emitted into the fuel 8. The ultrasonic pulse travels along the propagation path A indicated by the arrow in FIG. When the ultrasonic pulse reaches the reflection surface 42, the ultrasonic pulse is reflected by the reflection surface 42, and travels in the guide pipe 5 toward the liquid surface 81 along the propagation path B indicated by the arrow in FIG. 1. The ultrasonic pulse that has reached the liquid surface 81 is reflected by the liquid surface 81, reaches the ultrasonic element 3 again through the propagation path B, the reflection surface 42, and the propagation path A to vibrate the oscillation surface 31. Accordingly, the ultrasonic element 3 generates a voltage signal, and this voltage signal, that is, the reflected pulse detection signal is input to the arithmetic circuit 92.

  The arithmetic circuit 92 calculates the time from when the pulse generation circuit 91 generates a pulse voltage signal until the voltage signal due to the reflected pulse is detected. Based on this time, the arithmetic circuit 92 calculates the position of the liquid surface 81, that is, the liquid surface height H in FIG. Further, the remaining amount of fuel in the fuel tank 2 is calculated from the liquid level height H and the tank shape stored in advance as data.

  The drive circuit 93 corresponds to a signal for displaying the fuel remaining amount in the fuel tank 2 calculated by the arithmetic circuit 92 on the display unit 10, for example, a pointer shaft (not shown) corresponding to the fuel remaining amount in the fuel tank 2. A drive signal for rotating to an angle is output to the display unit 10. Thereby, the display unit 10 displays the remaining amount of fuel in the fuel tank 2.

  In the fuel liquid level detection device 1 according to the embodiment of the present invention described above, the guide pipe 4 and the guide pipe 5 are formed in a cylindrical shape in cross section and the inner diameters of both are equal.

  This prevents a decrease in ultrasonic propagation energy due to ultrasonic interference at the four corners of the cross-sectional square guide pipe of the conventional liquid level detection device, and suppresses changes in the cross-sectional area of the ultrasonic propagation path before and after the reflecting surface 42. Therefore, the level of the detection signal emitted from the ultrasonic element 3 due to the reflected wave from the liquid level can be increased, and the fuel liquid level detection device 1 capable of detecting the liquid level with higher accuracy can be realized.

Moreover, in the fuel level detecting device 1 according to the embodiment of the present invention described above, the thickness t ₁ of the guide pipe 4 and the thickness t ₂ of the guide pipe 5 are set to the fuel 8 in the guide pipe 4. The sound speed c ₁ in the middle and the sound speed c ₂ in the fuel 8 in the guide pipe 5 are set to be equal.

  When the ultrasonic wave propagates in the liquid, ultrasonic energy loss occurs when the ultrasonic wave propagation speed changes due to some cause, for example, a change in the shape and material of a pipe line through which the ultrasonic wave propagates. For this reason, in the fuel liquid level detection apparatus 1, the detection signal level emitted from the ultrasonic element 3 due to the reflected wave from the liquid level may be lowered, and it may be difficult to detect the liquid level with high accuracy.

  On the other hand, in the fuel level detecting device 1 according to the embodiment of the present invention, when the ultrasonic wave transits from the guide pipe 4 to the guide pipe 5, and when the ultrasonic wave transits from the guide pipe 5 to the guide pipe 4, No change in ultrasonic wave propagation speed. Therefore, the energy loss of the ultrasonic wave at the time of the transition between the guide pipe 5 and the guide pipe 4 is surely suppressed, the detection signal level generated by the ultrasonic oscillation element by the reflected wave from the liquid surface is increased, and the liquid level detection with high accuracy is performed. It is possible to realize a fuel level detecting device 1 that can

  In the fuel level detecting device 1 according to the embodiment of the present invention described above, the guide pipe 4 and the guide pipe 5 are formed from different materials. That is, the guide pipe 4 is formed from an aluminum die casting alloy, the guide pipe 5 is formed from a stainless steel pipe, and the guide pipe 5 is press-fitted and fixed to the guide pipe 4.

  As a result, by setting a plurality of types of the length L of the guide pipe 5, the fuel level detecting device 1 corresponding to the fuel tank 2 having different level heights when the tank is full can be easily and minimally increased in cost. Can be produced. In general, the shape of the fuel tank 2 of an automobile is different for each vehicle type because it is designed for each vehicle type. That is, the height of the liquid level 81 when the tank is full is also various, and the effect of configuring the fuel level detecting device 1 as described above is great.

In the fuel level detecting device 1 according to the embodiment of the present invention described above, the inner diameter dimension d ₁ of the guide pipe 4 (= the inner diameter dimension d ₂ of the guide pipe 5) is determined from the diameter D _{3 of the} oscillation surface 31. It is set small.

When the diameter d ₁ of the guide pipe 4 is larger than the oscillation surface 31 diameter D _{3 of the} ultrasonic element 3, that is, when the distance from the outer edge of the oscillation surface 31 to the inner wall of the guide pipe 4 is large, the ultrasonic wave is applied to the inner wall of the guide pipe 4. The rate of attenuation of ultrasonic energy until it reaches is increased. For this reason, the problem that the detection signal level which the ultrasonic element 3 emits by the reflected wave from the liquid level 81 becomes low arises.

Therefore, if the inner diameter d ₁ of the guide pipe 4 (= the inner diameter d ₂ of the guide pipe 5) is set smaller than the diameter D _{3 of} the oscillation surface 31, the energy of the ultrasonic wave emitted from the oscillation surface 31 is attenuated. It is possible to suppress the level of the detection signal emitted from the ultrasonic element 3 by the reflected wave from the liquid level 81 and realize the fuel level detecting device 1 capable of detecting the liquid level 81 with high accuracy.

  In the fuel level detecting device 1 according to the embodiment of the present invention described above, the guide pipe 4 is made of an aluminum die casting alloy and the guide pipe 5 is made of a stainless steel pipe. However, the material is limited to these materials. It is not necessary, and other materials may be combined as long as the material forming the guide pipe 4 and the guide pipe 5 is different.

  Further, in the fuel level detecting device 1 according to the embodiment of the present invention described above, the guide pipe 4 and the guide pipe 5 are formed from different materials, but may be formed from the same material. In that case, the guide pipe 4 and the guide pipe 5 may be integrally formed, or may be assembled after being formed as separate parts.

  Further, in the fuel liquid level detection device 1 according to the embodiment of the present invention described above, the shape of the reflection surface 42 is a simple flat surface, but this is concave, that is, both the oscillation surface 31 and the liquid surface 81. It is good also as a shape which is concave toward it.

  Moreover, although embodiment described above demonstrated the case where the liquid level detection apparatus for vehicles of this invention was applied to the fuel level detection apparatus 1 of a motor vehicle, it applied to other than the fuel level detection apparatus 1 as an example. Also good. In other words, it may be used for detecting the level of other liquids mounted on the vehicle, such as engine oil, brake fluid or window washer fluid. Furthermore, you may apply in order to detect the liquid level in the tank for liquid transportation with which the vehicle for liquid transportation was equipped.

1 is a partial cross-sectional view of a fuel level detecting device 1 according to an embodiment of the present invention. It is a schematic diagram explaining the electric circuit structure in the fuel liquid level detection apparatus 1 by one Embodiment of this invention.

Explanation of symbols

1 Fuel level detector (Vehicle level detector)
2 Fuel tank (tank)
21 Bottom (bottom)
3 Ultrasonic element (Ultrasonic oscillator)
31 Oscillating surface 4 Guide pipe (first cylinder)
41 Reflector (reflective member)
42 Reflecting surface 5 Guide pipe (second cylinder)
6 Bracket 7 Lead wire 8 Fuel (liquid)
81 Liquid level 9 Control circuit 91 Pulse generation circuit 92 Arithmetic circuit 93 Drive circuit 10 Display unit 11 Ignition switch 12 Battery A, B Propagation path d1
d2
D3
H Liquid level L Total length ΔL Length t1 Thickness t2 Thickness

Claims (4)

A tank for storing liquid;
An ultrasonic oscillator disposed at the bottom of the tank;
A reflection member including a reflection surface that reflects the ultrasonic wave emitted by the ultrasonic oscillation element toward the liquid level of the liquid in the tank;
In the vehicular liquid level detection device for detecting the liquid level position by receiving the reflected wave reflected from the liquid level of the ultrasonic wave emitted from the ultrasonic oscillation element by the ultrasonic oscillation element via the reflection surface. ,
A first cylindrical tube having a cross-sectional shape which is an ultrasonic wave propagation path between the ultrasonic oscillation element and the reflecting member;
A second cylindrical tube having a cross-sectional shape that is an ultrasonic wave propagation path from the reflecting member to the liquid surface ;
The inner diameter and the inner diameter of the second cylinder before Symbol first cylinder is formed to be almost equal,
The liquid level detection device for a vehicle according to claim 1, wherein an inner diameter of the first cylinder and an inner diameter of the second cylinder are formed smaller than a diameter of an oscillation surface that emits ultrasonic waves of the ultrasonic oscillation element . The liquid level detection device for a vehicle according to claim 1, wherein the first cylinder and the second cylinder are formed of the same material . 3. The vehicular liquid level detection apparatus according to claim 1, wherein the wall thickness of the first cylinder and the wall thickness of the second cylinder are formed to be substantially equal . 4. The first cylinder is made of an aluminum die casting alloy,
The second cylinder is made of a stainless steel pipe,
By setting the wall thickness of the second cylinder to 0.35 times the wall thickness of the first cylinder, the speed of sound in the fluid in the first cylinder and the liquid in the second cylinder The liquid level detecting device for a vehicle according to claim 1 , wherein sound speeds are made equal .

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