JP7659448B2 - Ultrasonic Sensor - Google Patents

Description

The present invention relates to ultrasonic sensors that are used in vehicle obstacle detection devices, automatic door systems, and various other devices.

In Japanese Patent Laid-Open Publication No. 10-123235, a short ring made of electrically conductive metal material such as copper is fitted coaxially from the outside through a retainer to the rear part of a housing that accommodates an ultrasonic vibrator as an ultrasonic sensor in which a coil that causes a resonance phenomenon together with an ultrasonic vibrator is not affected by fluctuations in the electromagnetic induction magnetic field as an external disturbance. The axial width of this short ring is set so as to cover all components including the transformer of the processing circuit through the rear part of the housing. The circuit board on which the processing circuit is mounted is arranged in the housing so as to extend in a direction perpendicular to the center line of the housing that passes through the ultrasonic vibrator. When the electromagnetic induction magnetic field as an external disturbance present in the vicinity of the ultrasonic sensor fluctuates, this electromagnetic induction magnetic field affects the coil of the transformer due to the fluctuation. For this reason, when the coil generates a back electromotive force due to its electromagnetic induction effect, this back electromotive force is output to the controller in a state in which it is added to the received signal as noise, and the controller erroneously detects the presence of an obstacle based on the received signal with the above noise added, even though there is no obstacle. In conventional ultrasonic sensors, a short ring is placed through a retainer to prevent the coil that causes the resonance phenomenon together with the ultrasonic transducer from being affected by fluctuations in the electromagnetic induction magnetic field as an external disturbance.

Japanese Patent Application Publication No. 10-123235

In the conventional structure, it is necessary to attach a retainer and short ring to the housing, which not only increases the number of parts but also increases the assembly man-hours and manufacturing costs. It was also found that electromagnetic induction fields act on the inside of the housing from parts not covered by the short ring and from gaps between the short ring and the outer surface of the housing, causing various noises. Furthermore, the conventional structure does not require the short ring to be grounded, but if grounding is to be done, it is necessary to devise a grounding structure. Another problem with the conventional structure is that mounting and installation of the circuit board is tedious.

The object of the present invention is to provide an ultrasonic sensor that can be constructed with a small number of parts and is less susceptible to the effects of electromagnetic induction fields.

In addition to the above objectives, another objective of the present invention is to provide an ultrasonic sensor that is easy to mount on a circuit board.

The present invention is directed to an ultrasonic sensor that includes an ultrasonic transducer housed in a resin housing and a circuit board that includes a coil housed in the housing and that forms a resonant circuit with the ultrasonic transducer, and transmits ultrasonic waves due to the piezoelectric effect of the ultrasonic transducer when a resonant voltage is applied to the ultrasonic transducer, and generates a received signal through the resonant circuit due to the inverse piezoelectric effect when the ultrasonic waves are reflected by an object and received by the ultrasonic transducer. In the ultrasonic sensor of the present invention, at least the inner surface of the housing is covered with a thin-film conductive layer. The thin-film conductive layer is electrically connected to an earth electrode on the circuit board. Therefore, according to the present invention, an ultrasonic sensor that is less susceptible to the effects of electromagnetic induction magnetic fields can be provided with a small number of parts. The thin-film conductive layer may be formed using an appropriate thin-film forming technique such as plating or vapor deposition. In particular, when the thin-film conductive layer is formed as a plated layer, the variation in the thickness of the thin-film conductive layer can be controlled, and the effects of the electromagnetic induction magnetic field can be minimized, and the presence of the thin-film conductive layer can be prevented from becoming an obstacle to assembly. For example, even if the plated layer is formed by electroless nickel plating, the thickness of the plated layer can be sufficiently secured to prevent the electromagnetic induction magnetic field from acting on the inside of the housing. All of the surfaces of the housing, including the inner surface, may be covered with a thin-film conductive layer. In this case, the outer surface of the housing is also covered with a plated layer, providing a double shielding effect.

Specifically, the housing may have a cylindrical main body and an annular wall portion disposed inside the cylindrical main body and protruding inward from the cylindrical main body. In this case, the surface of the annular wall portion is also covered with a thin-film conductive layer. An ultrasonic transducer is disposed in the forward space between one end of the cylindrical main body and the annular wall portion, and a circuit board is housed in the rear space between the other end of the cylindrical main body and the annular wall portion. With this structure, noise coming from the ultrasonic transducer side can be blocked to some extent by the annular wall portion covered with the thin-film conductive layer. The annular wall portion can also be used as a positioning means for the ultrasonic transducer and the circuit board, making it easier to assemble the ultrasonic sensor.

Furthermore, a pair of holding parts for holding a pair of opposing sides of the circuit board may be formed on the cylindrical body surrounding the rear space, and the surfaces of the pair of holding parts may also be covered with the thin-film conductive layer. A pair of earth electrode parts electrically connected to the thin-film conductive layer covering the surfaces of the pair of holding parts may be formed along the pair of sides of the circuit board. By adopting such a structure, not only is it easy to position and fix the circuit board, but the thin-film conductive layer can be grounded reliably. If the length of the earth electrode is increased and the entire holding part is connected to the earth electrode part, the grounding position of the thin-film conductive layer can be widened, and the occurrence of variations in the grounding effect due to differences in the grounding position can be prevented. The pair of holding parts can be composed of a pair of fitting grooves extending from the other end of the cylindrical body toward the annular wall part. If the pair of holding parts are composed of a pair of fitting grooves, the positioning of the circuit board is easy and the circuit board can be fixed reliably, so that the occurrence of connection failure can be prevented.

From the opening on the other end of the cylindrical body, multiple lead wires extend, each having a core wire connected to multiple connection electrodes on a circuit board, and a connector terminal may be connected to the core wires of the multiple lead wires. Providing a connector terminal via multiple lead wires increases the freedom of installation position of the ultrasonic sensor.

If the rear space is sealed with molded resin, waterproofing can be easily improved.

FIG. 2 is a perspective view of the ultrasonic sensor according to the embodiment in a vertical position. 2 is a cross-sectional view taken along line II-II in FIG. 1, in which the internal structure of the ultrasonic transducer and the molding resin are omitted. 4A and 4B are schematic diagrams showing the covering structure of a housing. 1 is a perspective view of an ultrasonic sensor according to an embodiment of the present invention, as viewed from a connector terminal side. 2 is an end view of line VV in FIG. 1. FIG. 2 is a bottom view of the ultrasonic sensor in the state shown in FIG. 1 . FIG. 13 is a diagram showing an example of an output of an ultrasonic sensor when a plating process is performed. FIG. 13 is a diagram showing an example of an output from an ultrasonic sensor when no plating process is performed. FIG. 13 is a diagram showing an example of an output of an ultrasonic sensor when a plating process is performed (when an object to be measured is present); FIG. 13 is a diagram showing an example of an output of the ultrasonic sensor when no plating process is performed (when an object to be measured is present);

Below, one embodiment of the ultrasonic sensor of the present invention will be described with reference to the drawings.

Figure 1 is a perspective view of an ultrasonic sensor 1 of this embodiment, which can be used in an obstacle detection device that functions as a corner sonar for vehicles, in a vertical position. However, the molded resin inside the housing 3 is omitted in Figure 1. Figure 2 is a cross-sectional view taken along line II-II in Figure 1, with the structure inside the ultrasonic transducer 5 and the molded resin omitted. Note that hatching indicating the cross-sectional portion is omitted in Figure 2. Figures 3(A) and (B) are schematic diagrams showing the covering structure of the housing 3. Figure 4 is a perspective view of the ultrasonic sensor 1 of this embodiment, as seen from the connector terminal 7 side. Figure 5 is an end view taken along line V-V in Figure 1, and Figure 6 is a bottom view in the state shown in Figure 1.

The ultrasonic sensor 1 is connected to a connector terminal 7 via three lead wires 9. The three lead wires 9 are soldered to connection electrodes included in the circuit pattern of a circuit board 13 housed inside the housing 3.

This ultrasonic sensor 1 is used by attaching it to, for example, the front bumper of a vehicle. The ultrasonic sensor 1 has a housing 3 formed from an insulating resin material such as PBT resin material. This housing 3 has a cylindrical main body 31 and an annular wall portion 32 disposed inside the cylindrical main body 31 and protruding inward from the cylindrical main body 31. An ultrasonic transducer 5 is disposed in a front space S1 between the tip (one end) of the cylindrical main body 31 and the annular wall portion 32, and a circuit board 13 is housed in a rear space S2 between the rear end (the other end) of the cylindrical main body 31 and the annular wall portion 32.

As shown in FIG. 3(A), in the ultrasonic sensor 1 of this embodiment, the inner surface 3A and the outer surface 3B of the housing 3 are covered with thin-film conductive layers 33 and 34. The thin-film conductive layers 33 and 34 may be formed using an appropriate thin-film forming technique such as plating or vapor deposition. In this embodiment, the entire inner surface 3A and the entire outer surface 3B of the housing 3 are covered with one or more plating layers such as electroless nickel plating. A preferred plating layer is made of electroless nickel plating or the like, and is a plating layer that blocks electrolytic noise and magnetic noise. The plating layer is thick enough to prevent the electromagnetic induction magnetic field from acting inside the housing 3.

The thin-film conductive layers 33 and 34 are electrically connected to an earth electrode on the circuit board 13, which will be described later. If the thin-film conductive layers 33 and 34 are formed of plated layers, the variation in the thickness of the thin-film conductive layers can be controlled, the influence of the electromagnetic induction magnetic field can be minimized, and the presence of the thin-film conductive layers can be prevented from hindering assembly. In particular, if the outer surface 3B of the housing 3 is also covered with a plated layer, as in this embodiment, a double shielding effect can be achieved. In addition, with such a structure, noise coming from the ultrasonic transducer 5 side can be blocked to some extent by the annular wall portion 32 covered with the thin-film conductive layer 33. The annular wall portion 32 can also be used as a positioning means for the ultrasonic transducer 5 and the circuit board 13, making the assembly of the ultrasonic sensor easier.

In this embodiment, a pair of fitting grooves 4 are formed in the cylindrical body 31 surrounding the rear space S2 as a pair of holding parts that hold a pair of opposing sides of the circuit board 13. As shown in FIG. 3B, the inner surfaces of the pair of fitting grooves 4 are also covered with a thin-film conductive layer 33. A pair of earth electrodes 14 are formed along a pair of sides of the circuit board 13 and electrically connected to the thin-film conductive layer 33 that covers the surfaces of the pair of fitting grooves 4. In this embodiment, the earth electrodes 14 are formed along the sides on the front and back surfaces of the circuit board 13 in the thickness direction. The present invention can also be realized by forming one earth electrode 14 along one side of the circuit board on one of the front and back surfaces of the circuit board 13 in the thickness direction. The electrical connection between the thin-film conductive layer 33 that covers the surfaces of the pair of fitting grooves 4 and the earth electrode 14 may be realized by strong contact, but it is preferable to join the two using solder or a conductive adhesive. When using solder, solder cream is applied to the earth electrode 14, and after fitting the circuit board 13 into the pair of fitting grooves 4, the entire structure is heated to melt the solder cream. This structure not only makes it easy to position and fix the circuit board 13, but also ensures that the thin-film conductive layer 33 is grounded. If the length of the earth electrode 14 is increased and the entire fitting groove 4 is connected to the earth electrode 14, the grounding position of the thin-film conductive layer 33 can be made wider, preventing variations in the grounding effect caused by differences in the grounding position.

Although not shown, the circuit board 13 is molded in the rear space S2 of the housing 3 with moisture-proof silicone resin (not shown). Meanwhile, the ultrasonic transducer 5 is coaxially molded in the front space S1 of the housing 3 with a vibration-absorbing elastic resin such as silicone rubber.

The ultrasonic transducer 5 is a commercially available product that is constructed by bonding a piezoelectric element inside an aluminum casing with an epoxy adhesive. If the entire inner and outer surfaces of the housing 3 are covered with a thin conductive layer as in this embodiment, the highest sealing effect can be provided for the components placed inside the housing, so even if an ultrasonic transducer 5 that does not have special noise countermeasures is used, it does not significantly affect its performance as an ultrasonic sensor.

The ultrasonic transducer 5 is connected to a resonant circuit on a circuit board 13 via a wire harness 15. Mounted on the circuit board 13 are a transformer 16 including a capacitor 19 and a coil that constitute the resonant circuit, and an IC 18 for signal processing. The secondary coil of the transformer 16 is used as a coil that constitutes the resonant circuit. In this embodiment, the signal processing circuit including the resonant circuit and the amplifier circuit mounted on the circuit board 13 adopts a known configuration.

The piezoelectric element (not shown) in the ultrasonic transducer 5 exerts a piezoelectric effect and an inverse piezoelectric effect, and this piezoelectric element is connected to the secondary coil of the transformer 16 via the wire harness 15. A parallel resonant circuit is formed including the piezoelectric element in the ultrasonic transducer 5, the capacitor 19, and the secondary coil of the transformer 16. When a drive voltage is applied to the primary coil of the transformer 16 under the control of the IC 18, the transformer 16 boosts the drive voltage, and the boosted drive voltage is generated in the secondary coil. As a result, mechanical vibration is generated due to the piezoelectric effect of the piezoelectric element in the ultrasonic transducer 5. As a result, the ultrasonic transducer 5 transmits ultrasonic waves forward from its transmission/reception surface 51 through the opening 35 of the housing 3. In addition, when this transmitted ultrasonic wave is reflected by an obstacle located in front, the ultrasonic transducer 5 receives the reflected ultrasonic wave at its transmission/reception surface 51 and transmits it to the piezoelectric element. Therefore, the piezoelectric element generates a piezoelectric voltage due to the inverse piezoelectric effect, and outputs this piezoelectric voltage to the amplifier circuit through the parallel resonant circuit.

In the above embodiment, the inner and outer surfaces of the housing 3 are all covered with a thin-film conductive layer made of a plated layer. Although it is possible to obtain the effects of the invention by covering at least the inner surface of the housing 3 with a thin-film conductive layer, from the viewpoint of the workability of plating, it is preferable to cover the inner and outer surfaces of the housing in their entirety with a plated layer.

7A is a diagram showing an example of the output of the ultrasonic sensor when the ultrasonic sensor of the present embodiment, in which the cylindrical body 31 is plated, is wrapped in a towel so as not to receive reflected waves, and a noise source is placed 30 cm away. FIG. 7B is a diagram showing an example of the output of the ultrasonic sensor when the ultrasonic sensor of the comparative example, in which the cylindrical body 31 is not plated, is wrapped in a towel so as not to receive reflected waves, and a noise source is placed 30 cm away. In FIGS. 7A and 7B, the horizontal axis is the distance (mm) from the ultrasonic sensor, and the vertical axis is the strength of the received radio wave. In FIGS. 7A and 7B, the large signal appearing near the distance 0 to near the distance 200 mm is the transmission signal of the ultrasonic sensor. The reason why the strength of the received radio wave from a distant position is large is because the amplification factor of the IC used is set to increase in proportion to the distance. This is also true in FIG. 7B. The received signals N and N' in FIGS. 7A and 7B correspond to the noise detected by the ultrasonic sensor. Comparing signals N and N' in Figures 7(A) and (B), the noise peak of the ultrasonic sensor of this embodiment is significantly smaller for the same noise source.

Figure 8 (A) is a diagram showing an example of the output S of the ultrasonic sensor when the object to be measured is placed at multiple locations in front of the ultrasonic sensor in which the cylindrical body 31 of the present embodiment is plated. Figure 8 (B) is a diagram showing an example of the output S' of the ultrasonic sensor when the object to be measured is placed in front of the ultrasonic sensor of the comparative example in which the cylindrical body 31 is not plated under the same conditions. S1 in Figure 8 (A) is a signal reflected from the object to be measured located closest to the ultrasonic sensor. The signal S'1 in Figure 8 (B) is also a signal reflected from the object to be measured located closest to the ultrasonic sensor, but its crest value is larger than that of the signal S1 in Figure 8 (A). This is because it contains noise. The crest value of the signal at the far position in Figure 8 (A) is also large. This is because it contains noise. Also, as can be seen by comparing the multiple signals Sd at the far position in FIG. 8(A) with the signal S'd at the far position in FIG. 8(B), the number of signals in the signal S'd at the far position in FIG. 8(B) is large, and there is no difference in the crest value of each signal, making it unclear which signal is the correct detection signal. Comparing FIG. 8(A) and (B) shows that the ultrasonic sensor of the embodiment of the present invention is less susceptible to the effects of noise and can correctly detect the presence of the object to be measured.

The present invention provides an ultrasonic sensor that uses a small number of parts and is less susceptible to the effects of electromagnetic induction fields.

REFERENCE SIGNS LIST 1 Ultrasonic sensor 3 Housing 3A Inner surface 3B Outer surface 31 Cylindrical body 32 Annular wall portion 33, 34 Thin-film conductive layer 35 Opening 4 Fitting groove (holding portion)
5 ultrasonic transducer 7 connector terminal 9 lead wire 13 circuit board 14 earth electrode portion 15 wire harness 16 transformer 18 IC
19 Condenser S1 Front space S2 Rear space

Claims (8)

An ultrasonic sensor comprising an ultrasonic transducer housed in a resin housing, and a circuit board having a coil housed in the housing and constituting a resonant circuit with the ultrasonic transducer, wherein when a resonant voltage is applied to the ultrasonic transducer, an ultrasonic wave is transmitted by the piezoelectric effect of the ultrasonic transducer, and when the ultrasonic wave is reflected by an object and received by the ultrasonic transducer, a reception signal is generated through the resonant circuit by the inverse piezoelectric effect,
At least the inner surface of the housing is covered with a thin conductive layer;
4. An ultrasonic sensor comprising: a thin-film conductive layer electrically connected to a ground electrode on the circuit board; The ultrasonic sensor according to claim 1, characterized in that all of the surfaces of the housing, including the inner surface, are covered with the thin-film conductive layer. The housing includes a cylindrical main body having a cylindrical shape and an annular wall portion disposed inside the cylindrical main body and protruding inward from the cylindrical main body,
the surface of the annular wall portion is also covered with the thin-film conductive layer;
The ultrasonic transducer is disposed in a front space between one end of the cylindrical body and the annular wall portion,
3. The ultrasonic sensor according to claim 1, wherein the circuit board is accommodated in a rear space between the other end of the cylindrical body and the annular wall portion. a pair of holding portions for holding a pair of opposing sides of the circuit board are formed on the cylindrical main body surrounding the rear space,
The surfaces of the pair of holding parts are also covered with the thin film conductive layer,
4. The ultrasonic sensor according to claim 3, further comprising a pair of earth electrodes formed along the pair of sides of the circuit board, the pair of earth electrodes being electrically connected to the thin-film conductive layer covering the surfaces of the pair of holding portions. The ultrasonic sensor according to claim 4, wherein the pair of holding portions is a pair of fitting grooves extending from the other end of the cylindrical body toward the annular wall portion. The ultrasonic sensor according to claim 3, wherein a plurality of lead wires, each having a core wire connected to a plurality of connection electrodes on the circuit board, extend from the opening on the other end of the cylindrical body, and connector terminals are connected to the core wires of the plurality of lead wires. An ultrasonic sensor as described in claim 3, in which the rear space is sealed with molding resin. The ultrasonic sensor according to claim 1, wherein the thin-film conductive layer is a plated layer.

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