JPH076938B2 - Water drop detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a water droplet detection device for detecting water droplets such as raindrops, and particularly to detect water droplets based on a change in capacitance between detection electrodes due to adhesion of water droplets. And what to do.

[Conventional technology]

As a conventional electrostatic capacitance type water droplet detection device, one detector including a pair of detection electrodes insulated from each other is provided at a water droplet attachment position. Then, the oscillation frequency of the RC oscillator is changed by the change in the capacitance of this detector.
Adhesion of water droplets is determined by the change in the oscillation frequency.

[Problems to be solved by the invention]

In the conventional device, for example, when detecting rainfall, it is possible to detect rainfall with excellent detection sensitivity at the beginning of rainfall. However, as the rainfall time becomes longer, more raindrops adhere to the detector, the capacitance increases, and the oscillation frequency of the oscillation circuit becomes saturated.

Therefore, even if a new water drop is attached and the capacitance changes, the oscillation frequency of the oscillation circuit changes only slightly.

That is, it becomes difficult to distinguish between the attachment of new water droplets due to rainfall and the water droplets already attached due to rainfall.

The present invention has been made in view of the problems as described above, and an object thereof is to provide a water droplet detection device capable of detecting the attachment of further raindrops with excellent sensitivity even if a large amount of raindrops are attached. There is a place to do it.

[Means for solving problems]

Therefore, in order to achieve the above-mentioned object, the present invention provides a first detector including a pair of detection electrodes provided at a water droplet attachment position and a second detection including a pair of detection electrodes provided at the attachment position. A detector, an oscillating circuit in which an oscillating frequency changes according to a difference in capacitance between respective detection electrodes of the first detector and the second detector, and a change amount of the oscillating frequency is detected. The technical means of including a determination means for determining the adhesion of water droplets is adopted.

[Action]

The water drop detection device according to the present invention comprises two detectors.

When a water droplet adheres to one of the two detectors, the difference in capacitance between the two detectors changes. The oscillation frequency of the oscillation circuit changes according to the change in the difference in capacitance.

Then, the determination means detects the amount of change in the oscillation frequency and determines the attachment of water droplets.

If a large amount of water droplets adhere to these two detectors, 2
Water droplets adhering to one detector randomly attach, so 2
The difference in capacitance between the two detectors is almost the same as in the state where no water droplets are attached. Therefore, the oscillating frequency of the oscillating circuit is not saturated, and is almost the same as the oscillating frequency when the water droplets are not attached. From this state,
A new water droplet is attached to one of the detectors,
If the difference between the electrostatic capacities of the two detectors changes even if it is small, the oscillation frequency of the oscillation circuit changes greatly.

Then, the judging means judges the adhesion of the water droplet based on the change in the oscillation frequency.

〔The invention's effect〕

As described above, the water droplet detection device according to the present invention can detect the attachment of a new water droplet with excellent sensitivity without saturating the oscillation frequency even when a large amount of water droplets are attached.

〔Example〕

Hereinafter, a raindrop sensing type wiper control device for a vehicle, which is an embodiment to which the present invention is applied, will be described.

This raindrop sensing type wiper control device detects the attachment of raindrops by a raindrop sensor provided in front of a windshield of a vehicle or the like. Then, when a raindrop is detected, the wiper of the vehicle is driven, and the wiper is stopped when the raindrop is no longer attached.

First, the structure of this embodiment will be described with reference to FIGS.

FIG. 1 is a circuit configuration diagram of this embodiment. Oscillator circuit 9
Is four inverter gates 10,11,1 connected in series
2, 13, a resistor 14, and detection capacitors 15a, 15b corresponding to the first detector and the second detector. The configuration of the detection capacitors 15a and 15b will be described later. The oscillation output 9a of the oscillation circuit 9 is sent to the wiper controller 16 by the wire harness 1b.

The wiper controller 16 is a one-shot circuit 20, f-V
It is composed of a conversion circuit 23, a voltage comparison circuit 26, a monostable multivibrator 29, a drive circuit 33, a constant voltage circuit 35, a power-on reset circuit 36, and the like.

FIG. 2 shows the detection capacitors 15a and 15b and the oscillator circuit 9.
FIG. 3 is a partial cutaway view of a sensor unit incorporating the.

1 is a sensor part, 1a is a resin-molded housing,
1b is a harness for electrically connecting the sensor unit 1 and the wiper controller. A circuit board 1c on which the oscillator circuit 9 is mounted is built in and fixed in the housing 1a. On the slope of the housing 1a, a detection electrode substrate 1d made of an insulating ceramic, on which detection capacitors 15a and 15b are formed, is provided for waterproofing.
It is fitted through the ring le. The detection capacitors 15a and 15b of the detection electrode substrate 1d are connected to the oscillation circuit 9 mounted on the circuit substrate 1c by the lead wire 1f.

FIG. 3 is a view taken in the direction of arrow A in FIG. 2 showing an electrode pattern forming the detection capacitors 15a and 15b of this embodiment.

FIG. 4 is a sectional view taken along the line BB ′ of FIG.

On the surface of the detection electrode substrate 1d, there are comb-shaped detection electrodes 2a and 2b.
Is formed, and the common electrode 2c is formed so as to sew between the detection electrodes 2a and 2b. These detection electrodes 2a, 2b,
The common electrodes 2c are insulated from each other, and the coating film 2d is formed so as to cover them. And the detection electrodes 2a, 2b,
Each of the common electrodes 2c is connected to the lead wire 1f through a hole (not shown) formed in the detection electrode substrate 1d. That is, the detection capacitor 15a is formed between the detection electrode 2a and the common electrode 2c, and the detection capacitor 15a is formed between the detection electrode 2b and the common electrode 2c.
15b is formed.

The sensor unit 1 configured in this manner is fixed to a position such as a vehicle hood where raindrops fly, with the slope of the sensor unit 1 facing forward.

Due to this slope, raindrops attached to the surface of the detection electrode substrate 1d immediately drop.

Next, the operation of this embodiment will be described with reference to the drawings.

First, when raindrops adhere to the surface of the detection electrode substrate 1d, the detection electrode 2a and the common electrode 2c, or the detection electrode 2b and the common electrode 2c.
Either of them increases the capacitance. That is, the capacitance of either the detection capacitor 15a or the detection capacitor 15b becomes large.

As a result, the difference between the electrostatic capacitance C ₁ of the detection capacitor 15a and the electrostatic capacitance C ₂ of the detection capacitor 15b changes, and the oscillation frequency of the oscillation circuit 9 changes.

FIG. 5 is an oscillation characteristic diagram showing the characteristics of the difference in capacitance (C ₁ -C ₂ ) of the two capacitors connected to the oscillation circuit 9 and the oscillation frequency.

In this embodiment, (C ₁ -C ₂ ) = 0 was set when there was no rainfall, but (C ₁ -C ₂ ) may be an appropriate value. This (C ₁ −
If the oscillation frequency when C ₂ ) = 0 is the reference frequency f ₀ ,
The range in which the oscillation frequency changes according to this embodiment is Bb.

In the case of the one described in the section of the conventional technique, (C ₁ −C ₂ ) increases with the attachment of raindrops due to rainfall, and the band in which the oscillation frequency changes is larger than that in this example as shown by Ba. Get wider

FIG. 6 is a characteristic diagram showing changes in the oscillation frequency of the oscillation circuit 9 with the passage of rainfall time from the beginning of rainfall.

In FIG. 6, the change shown in (B) is due to this embodiment, and the change shown in (A) is the case described in the section of the prior art using only one detection capacitor. .

In the case of the conventional one, the number of attached raindrops increases and the oscillation frequency decreases as the rainfall time elapses. Eventually,
When the newly attached raindrops and the raindrops falling from the detection electrode substrate balance, the decrease in the oscillation frequency becomes saturated. Then, the change in the oscillation frequency due to newly attached raindrops becomes small.

However, according to this embodiment, even if the number of raindrops attached increases with the passage of rainfall time, the number of raindrops that affect the electrostatic capacitances of the two detection capacitors 15a and 15b can be regarded as substantially the same.

Therefore, the difference between the electrostatic capacities of the two detection capacitors 15a and 15b does not change significantly, but only increases or decreases with the difference in the absence of raindrops as a result of the attachment of new raindrops. Therefore, the oscillation frequency of the oscillation circuit 9 also increases / decreases in the band Bb around the reference frequency f ₀ with the attachment of new raindrops.

In this way, the deposition frequency of raindrops on the detection electrode substrate 1d changes the oscillation frequency of the oscillation output 9a of the oscillation circuit 9. The oscillation frequency 9a is sent to the controller 16 and input to the one-shot circuit 20 through a low pass filter composed of a resistor 18 and a capacitor 19. Output 20 of one-shot circuit 20
a is a pulse having a constant time width determined by the time constant of the resistor 21 and the capacitor 22, and this output 20a is converted into a voltage output 23a by the fV conversion circuit 23. Now, when the oscillation output 9a of the oscillation circuit 9 changes, the voltage output 23a of the fV conversion circuit 23 also changes correspondingly, and the differentiating circuit 2 which inputs this
5 outputs the change 23b of the voltage output 23a to the voltage comparison circuit 26. When the change 23b from the differentiating circuit 25 exceeds a predetermined comparison voltage 26a, the output 27a of the comparator 27 is inverted from high level to low level. This signal is inverted again by the inverter gate 28 and the D flip-flop.
Since it is input to the clock terminal ck of 30, the clock terminal ck
Input 29a rises from low level to high level.
Therefore, the output pulse 29b of the monostable multivibrator 29
Turns on the NPN transistor 34 of the drive circuit 33 and closes a relay for energizing a wiper motor (not shown) to drive the wiper.

FIG. 7 is a characteristic diagram showing the fV conversion characteristic of the fV conversion circuit.

The oscillation frequency band according to the conventional technique described in FIG.
, And according to this example is designated as Bb. When the band in which the oscillation frequency changes is Ba, the fV characteristic becomes the curve shown in (A), and when it is Bb, the fV characteristic becomes the curve shown in (B).

According to this embodiment, a large change in the output voltage can be obtained by a slight change in the oscillation frequency. Further, according to the conventional technique, the oscillation frequency is saturated due to the decrease in the oscillation frequency, and the change in the output voltage with respect to the change in the oscillation frequency is also saturated due to the fV characteristic. However, in this embodiment, the oscillation frequency hardly changes from the reference frequency f _0, and therefore the fV characteristic is not saturated.

As described above, according to the above-described embodiment, even if a large amount of raindrops adhere to the detection electrode substrate, the oscillation frequency of the oscillation circuit will not be saturated. Therefore, if new raindrops are attached, the capacitances C ₁ and C _{2 of the} two detection capacitors 15a and 15b are increased.
The difference (C ₁ −C ₂ ) in the value changes even if it is small, and a large change in the oscillation frequency is obtained.

Further, in the fV conversion circuit, the band of the oscillation frequency can be set narrow, and a small change in the oscillation frequency can be output as a large voltage change.

As described above, in this embodiment, even if a large amount of raindrops adhere to the detection electrode substrate due to rainfall, it is possible to detect the attachment of new raindrops with high sensitivity.

8 and 9 show another embodiment to which the present invention is applied.

FIG. 8 is a circuit configuration diagram of this embodiment.

FIG. 9 is a view taken in the direction of arrow A in FIG. 2 showing an electrode pattern which constitutes the detection capacitors 15a and 15b of this embodiment.

In the above-described embodiment, the f-V conversion circuit is used to convert the change in the oscillation frequency into the change in the voltage to detect the attachment of water drops (raindrops). However, in this embodiment, a PLL circuit is used to convert a change in the oscillation frequency into a phase change to detect a water drop.

The electrode patterns forming the detection capacitors 15a and 15b are provided with two common electrodes 2c facing the detection electrodes 2a and 2b, respectively. As a result, the two detection capacitors are completely insulated from each other, and one water drop does not affect both detection capacitors. In addition, it is possible to prevent the water droplets from alternately affecting the two detection capacitors in the process of sliding down the slope of the sensor unit 1.

The oscillation output 9a of the oscillation circuit 9 is input to the PLL circuit 42. PLL
The phase output 42a of the circuit 42 is a pulse train having a pulse width corresponding to the phase change associated with the change of the oscillation output 9a. The counter 41 is normally reset by the phase output 42a.
The phase is changed by the change of the oscillation output 9a and the reset is released only when the pulse width is changed, and the output pulse 40a of the reference oscillator 40 is counted. The pulse width of the phase output 42a is
If the time width of the counter 41 is sufficient to output the output 41a, the output 41a generates a pulse, the monostable multivibrator 29 is triggered, and the drive circuit 33 operates.

In this embodiment, similarly to the fV conversion circuit of the above-described embodiments, the band of the oscillation frequency that is the input of the PLL circuit 42 can be narrowed, and the pulse width of the phase output can be greatly changed with a small change of the oscillation frequency. Can be changed. Thereby, the detection sensitivity can be increased.

In addition to the two embodiments described above, two capacitances C ₁ , C
₂ may be formed on two separate detection electrode substrates. Further, although ceramic is shown as the detection electrode substrate for forming the detection electrode, a substrate such as glass epoxy may be used, and the coating film may be a green mask, Teflon coating or the like as long as it has an insulating property.

Further, the electrode patterns forming the two detection capacitors 15a and 15b are not limited to the comb-teeth pattern, and any electrode pattern whose capacitance changes due to the attachment of water droplets may be used. For example, it is a concentric electrode pattern.

Further, the present invention is not limited to actuating a wiper of a vehicle, a ship, or the like, and the present invention may be applied as a household or industrial rain detector or a water drop detector.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment to which the present invention is applied, and FIG.
FIG. 3 is a partially cutaway view of a sensor section of one embodiment, FIG. 3 is a view showing an electrode pattern of one embodiment in the direction of arrow A of FIG. 2, and FIG. 4 is a third view showing a configuration of an electrode pattern of one embodiment. FIG. 5 is a characteristic diagram for explaining the operation of one embodiment, FIG. 8 is a circuit configuration diagram of another embodiment, and FIG. 9 is another. FIG. 2B is a diagram showing an electrode pattern of the embodiment as viewed from the direction of arrow A in FIG. 1 …… Sensor part, 1a …… Housing, 1d …… Detection electrode board, 1C …… Circuit board, 2a, 2b …… Detection electrode, 2c …… Common electrode, 9 …… Oscillation circuit, 15a, 15b …… Detection Capacitor, 16 ……
Wiper control, 20 …… One-shot circuit, 23 ……
f-V conversion circuit, 25 ... Differentiation circuit, 26 ... Voltage comparison circuit, 2
9 …… Monostable multivibrator, 33 …… Drive circuit, 35…
… Constant voltage circuit, 36 …… Power-on reset circuit, 40 …… Reference oscillation circuit, 41 …… Counter, 42 …… PLL circuit.

Front page continuation (72) Inventor Hiroaki Nishimura 1-1, Showa-cho, Kariya city, Aichi prefecture, Nihon Denso Co., Ltd. (72) Inventor Tatsuhiko Nimura, 1-1, Showa-cho, Kariya city, Aichi prefecture, Nihondenso Co., Ltd.

Claims (1)

[Claims] 1. A first detector including a pair of detection electrodes provided at a water drop attachment position, and a second detector including a pair of detection electrodes provided at the attachment position.
Of the detector, an oscillating circuit in which the oscillating frequency changes in accordance with the difference in the capacitance between the detection electrodes of the first detector and the second detector, and the amount of change in the oscillating frequency. A water droplet detection device, comprising: a determination unit that detects and determines whether or not the water droplet is attached.