JP2018128331A - Liquid level detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid level detector whose accuracy of detecting a liquid level is not reduced even when a power supply voltage changes.SOLUTION: A liquid level detector F comprises: a propagation part 1 immersed in liquid L; a piezoelectric element 2a fixed to the propagation part 1; a transmission circuit 2b for driving the piezoelectric element 2a; a reception circuit 2c for detecting vibration of the piezoelectric element 2a; and a position detection part 3 for driving the transmission circuit 2b and detecting a position of a liquid surface LS of the liquid L on the basis of an output signal of the reception circuit 2c. In the liquid level detector F, a constant voltage circuit 2d is provided for supplying a predetermined voltage to the transmission circuit 2b by receiving power supply from a battery mounted on a vehicle. Even when a battery voltage changes, vibration of the piezoelectric element 2a caused by the transmission circuit 2b is made constant by the constant voltage circuit 2d. Thereby, accuracy of detecting a liquid level is not reduced.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a liquid level detection apparatus using ultrasonic waves.

  A conventional liquid level detection apparatus using ultrasonic waves is disclosed in Patent Document 1. This liquid level detection device detects the liquid level of the liquid based on the propagation time of the surface wave generated when the propagation part in the liquid is vibrated.

JP-A-2016-138850

  However, particularly when such a liquid level detection device is driven by supplying power from a vehicle battery, the detection accuracy may be reduced due to the influence of voltage fluctuation.

  The present invention has been made in view of the above-described problems, and it is an object of the present invention to provide a liquid level detection device in which the detection accuracy of the liquid level position does not decrease due to fluctuations in power supply voltage.

The liquid level detection device according to the present invention is:
A propagation part immersed in a liquid;
A piezoelectric element fixed to the propagation part;
A transmission circuit for driving the piezoelectric element;
A receiving circuit for detecting vibration of the piezoelectric element;
A position detection unit that drives the transmission circuit and detects the position of the liquid level based on the output signal of the reception circuit;
In a liquid level detection device comprising:
A constant voltage circuit for receiving a power supply from a battery mounted on the vehicle and supplying a predetermined voltage to the transmission circuit is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the liquid level detection apparatus by which the detection precision of a liquid level position does not fall by the fluctuation | variation of a power supply voltage can be provided.

1 is a schematic configuration diagram of a liquid level detection device according to an embodiment of the present invention. The side view of the propagation part of the same liquid level detection apparatus. The block diagram which shows the transmission / reception circuit of the liquid level detection apparatus. The wave form diagram which shows the surface wave and internal propagation wave of the liquid level detection apparatus.

  Below, with reference to an accompanying drawing, liquid level detection device F which is an embodiment of the present invention is explained.

  As shown in FIGS. 1 and 2, the liquid level detection device F includes a propagation unit 1, a vibration generation detection unit 2, and a position detection unit 3, and detects the liquid level of a fuel tank mounted on the vehicle. To do.

  The propagation unit 1 is immersed in a liquid L (medium such as gasoline or alcohol) stored in a fuel tank (not shown).

  The propagation part 1 is a material capable of satisfactorily propagating vibrations, and is made of, for example, a synthetic resin mainly composed of polyphenylene sulfide (PPS) resin. The shape of the propagation part 1 is a quadrangular column (columnar body) having a flat propagation surface through which a surface wave W1 described later propagates. The propagation part 1 is formed with a groove 1a in which a part thereof is cut out, and the groove 1a includes an internal propagation wave reflection part 1b that reflects an internal propagation wave to be described later.

  The vibration generation detection unit 2 is a vibration generation unit that applies vibration to the propagation unit 1 and is also a vibration detection unit that detects vibration of the propagation unit 1.

  The piezoelectric element 2a is a surface in which the groove 1a is not provided to the other end of the propagation part 1 in order to generate the surface wave W1 and the internal propagation wave W2 in the propagation part 1 and to detect the surface wave W1 and the internal propagation wave W2. The piezoelectric element 2a is installed so as to protrude. The propagation unit 1 and the piezoelectric element 2a are fixed in close contact. With this configuration, the piezoelectric element 2 a generates vibration on the propagation unit 1 to generate a surface wave W1 on the surface of the propagation unit 1 and an internal propagation wave W2 inside the propagation unit 1. Furthermore, the vibration of the propagation part 1 (vibration by the surface wave W1 and the internal propagation wave W2) is detected, converted into a voltage and output. The surface wave W1 is, for example, a Rayleigh wave, a leaky Rayleigh wave, a transverse surface acoustic wave, or the like, and the internal propagation wave W2 is, for example, a transverse wave.

  The transmission circuit 2b drives and excites the piezoelectric element 2a. The transmission circuit 2b includes, for example, a drive circuit and a transformer. The transmission circuit 2b applies a voltage to the piezoelectric element 2a by the drive signal S1 output at a predetermined cycle output from the position detection unit 3.

  The receiving circuit 2 c detects vibration based on the voltage generated by the piezoelectric element 2 a and outputs a detection signal to the position detection unit 3. The receiving circuit 2c includes an input protection circuit CD1, an amplifier circuit CD2, a band pass filter CD3, and a waveform shaping circuit CD4.

  The input protection circuit CD1 is composed of a diode, for example. The input protection circuit CD1 prevents the reception circuit 2c from being damaged.

  The amplifier circuit CD2 is composed of, for example, an operational amplifier and a resistor that adjusts the amplification degree of the application amplifier. Since the amplification of the vibration detected by the piezoelectric element 2a varies depending on the length of the propagation unit 1, it is preferable that the amplification factor of the operational amplifier can be adjusted by the resistance value of the resistor according to the length of the propagation unit 1. .

  The band pass filter CD3 removes signals other than the frequency band of the signal detected by the piezoelectric element 2a. Thereby, the vibration noise in the case where the propagating body 1 itself is physically shaken from the outside due to vibration caused by traveling of the vehicle or the like can be removed.

  The waveform shaping circuit CD4 is an amplitude operation circuit that outputs a part of the input waveform. The waveform shaping circuit CD4 shapes the signal output from the bandpass filter CD3 into a waveform that can be easily detected by the position detection unit 3 and outputs the waveform.

  The constant voltage circuit 2d transforms the power supplied from the battery mounted on the vehicle into a predetermined voltage and supplies it to the transmission circuit 2b. The constant voltage circuit 2d is a constant voltage circuit using, for example, a Zener diode (constant voltage diode), a linear regulator, or a switching type DC stabilized power supply circuit. Even if the voltage of the battery as a power source fluctuates, the constant voltage circuit 2d drives the transmission circuit 2b with a stable voltage. Therefore, the intensity of the vibration V1 generated by the piezoelectric element 2a is constant and the detection accuracy is stabilized. .

  The position detection unit 3 is a meter that displays various measurement values such as a traveling speed of a vehicle including a control unit such as a microcontroller. The position detection unit 3 outputs the drive signal S1 to drive the transmission circuit 2b, and detects the vibration of the propagation unit 1 output from the reception circuit 2c to detect the liquid level LS of the liquid L.

  The vibration which arises in the propagation part 1 is demonstrated using FIG. 4 shown typically. In FIG. 4, the leftmost vibration is the vibration V <b> 1 generated by the piezoelectric element 2 a by the drive signal S <b> 1 output from the position detection unit 3. The second vibration from the left is the vibration V2 of the surface wave W1 that propagates through the propagation part 1 and is reflected by the internal propagation wave reflection part 1b of the propagation part 1 and returns. The rightmost vibration is the vibration V <b> 3 of the surface wave W <b> 1 that has propagated through the surface of the propagation unit 1, reflected at the other end of the propagation unit 1, and returned.

  The position detection unit 3 estimates the temperature of the propagation unit 1 from the propagation time T1 from the time t1 when the vibration V1 occurs to the time t2 when the vibration V2 occurs. Then, the liquid level LS of the liquid L is detected based on the post-correction propagation time obtained by correcting the propagation time T2 at the time t3 when the vibration V3 is generated from the time t1 to the estimated temperature.

As described above, the liquid level detection device of the present invention includes the propagation part 1 immersed in the liquid L, the piezoelectric element 2a fixed to the propagation part 1, the transmission circuit 2b for driving the piezoelectric element 2a, and the piezoelectric element 2a. In a liquid level detection device F including a reception circuit 2c that detects vibration and a position detection unit 3 that drives the transmission circuit 2b and detects the position of the liquid level LS of the liquid L based on an output signal of the reception circuit 2c. A constant voltage circuit 2d that receives a power supply from a battery mounted on the vehicle and supplies a predetermined voltage to the transmission circuit 2b is provided.
With this configuration, it is possible to provide a liquid level detection device in which the detection accuracy of the liquid level position does not decrease due to fluctuations in the power supply voltage.

  The present invention is not limited to the above-described embodiment, and may be changed (including deletion of components) without departing from the gist of the invention.

  The present invention relates to a liquid level detection device, and in particular, can be used for a liquid level detection device that detects a liquid level using ultrasonic waves.

  F ... Liquid level detection device, L ... Liquid, LS ... Liquid level, S1 ... Drive signal, T1 ... Propagation time (internal propagation wave W2), T2 ... Propagation time (surface wave W1), V1 ... Vibration, V2 ... Vibration ( Internal propagation wave), V3 ... vibration (surface wave), W1 ... surface wave, W2 ... internal propagation wave, 1 ... propagation unit, 2 ... vibration generation detection unit, 2a ... piezoelectric element, 2b ... transmission circuit, 2c ... reception circuit , 2d ... Constant voltage circuit

Claims (1)

A propagation part immersed in a liquid;
A piezoelectric element fixed to the propagation part;
A transmission circuit for driving the piezoelectric element;
A receiving circuit for detecting vibration of the piezoelectric element;
A position detection unit that drives the transmission circuit and detects the position of the liquid level based on the output signal of the reception circuit;
In a liquid level detection device comprising:
A constant voltage circuit for receiving a power supply from a battery mounted on the vehicle and supplying a predetermined voltage to the transmission circuit is provided.
A liquid level detection device characterized by that.

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