JPS6175251A - Water drop detection sensor - Google Patents

Abstract

PURPOSE:To detect a water drop positively, by providing a detection electrode plate comprising an electrode surface having a detection electrode and a ground electrode and a detection surface for detecting the attaching of a water drop to detect the water drop depending on changes in the electrostatic capacitance between both of the electrodes. CONSTITUTION:A detection elecrode plate 1 is made up of a detection surface comprising the surface of the top surface of a case 8 of a water drop detection sensor contacting a glass plate 7 and an electrode surface formed by providing a detection electrode 1a, a subelectrode 1b and a ground electrode 1c on the back of the top surface. Then, an oscillation circuit 2 and a detection circuit 3 are provided in the case 8 while the oscillation frequency is set at such a band with as to ensure that the variation in the output voltage due to a water drop is larger than the variation in the output voltage due to a water film. Any water drop attached to the glass plate 7 will lower the output of a detection circuit 3 thereby enabling the detection of possible water drop. This assures a positive detection of the water drop without being affected by external noises, vibration of a vehicle and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a water droplet detection sensor used for driving a wiper of a vehicle or the like.

[Prior art and its problems]

Window cleaners installed in vehicles and the like are configured to operate at a constant speed or intermittently.

However, it is preferable that the operation be performed automatically depending on the adhesion of raindrops to the glass surface, and that the speed is also variable.

An example of such a sensor for detecting water droplets on a glass surface is one in which a piezoelectric detection element is placed on the hood of a vehicle, as shown in Nissan Technical Report, December 1980 (No. 19), page 97. It has been known. This water drop detection sensor uses a piezoelectric detection element to detect vibrations caused by falling raindrops as an electrical signal and sends it to an integrating circuit.When the level reaches a certain value, it operates the wiper and resets the integrating capacitor. be.

However, such a water droplet detection sensor may malfunction due to vibrations of the vehicle or external noise such as a horn. Additionally, it is necessary to operate the wipers when it snows, but since the piezoelectric detection element is installed on the hood of the vehicle, if snow accumulates on the hood, it will not be able to detect the snow, and the wipers will no longer operate. there were.

Another option is to use a photoelectric sensor instead of a piezoelectric sensor to detect raindrops on the glass surface, but it is difficult to detect only raindrops because the surrounding brightness changes significantly, and it is difficult to detect only raindrops on the glass surface. There is a problem in that sufficient detection is not possible when raindrops adhere to the sensor.

[Purpose of the invention]

The present invention has been made in view of the problems of conventional water droplet detection sensors, and an object of the present invention is to provide a water droplet detection sensor that can detect water droplets adhering to a detection surface by changes in capacitance. do.

[Structure and effects of the invention]

The present invention includes a sensing electrode plate having a sensing electrode and a ground electrode adjacent to the sensing electrode on an electrode surface, and the other surface serving as a sensing surface for detecting adhesion of water droplets, and static electricity between the electrodes of the sensing electrode plate. The oscillation circuit consists of a resonant circuit including capacitance, and the oscillation frequency is set to a frequency where the amplitude change due to the presence or absence of water droplets on the detection surface of the detection electrode plate is larger than the amplitude change due to the presence or absence of a water film. The present invention is characterized in that it includes a detection circuit for detecting, and detects adhesion of water droplets by a change in capacitance of a detection electrode plate.

According to the present invention having such characteristics, the oscillation amplitude is detected by changes in the capacitance of the detection electrode plate, and the presence or absence of water droplets adhering to the detection surface is detected. I never receive it. In addition, the oscillation frequency of the oscillation circuit is selected such that the amount of change due to the presence or absence of water droplets is greater than the amount of change due to the presence or absence of a thin water film, and since water droplets are detected based on the amplitude change, the thin water remaining after the wiper operation is detected. It becomes possible to reliably detect only water droplets, not the film. Therefore, if this water droplet detection sensor is used to drive the wiper of a vehicle, the wiper can be operated at high or low speeds depending on the amount of water droplets, making it possible to maintain a constant visibility on the glass surface of the vehicle.

[Explanation of Examples]

FIG. 1 is a circuit diagram showing an embodiment of a water droplet detection sensor according to the present invention. In this figure, the detection electrode plate 1 is the oscillation circuit 2.
It oscillates at a predetermined frequency due to its capacitance, and its output is detected by the detection circuit 3. As shown in FIG. 2, the sensing electrode plate l has an elongated elliptical sensing electrode 1a in the center and an annular sub-electrode 1b surrounding the sensing electrode 1a.
It has Then, an auxiliary electrode 1 is placed on the outer periphery of the detection electrode plate 1.
A ground electrode IC is provided at a certain distance from b and surrounding them in an annular manner. The other surface of the detection electrode plate 1 is configured as a detection surface to which water or the like may adhere directly or via a glass plate or the like.

These three electrodes 1a-1c are connected to terminals 4, 5.6 shown in FIG. 1, respectively. Here, in the detection electrode plate 1, if the capacitance between the detection electrode 1a and the sub-electrode lb is 01, and the capacitance between the detection electrode 1a and the ground electrode 10 is 02, then each capacitance is equal to that of the oscillation circuit 2. The zero oscillation circuit 2, which will be connected in parallel to the resistors R1 and R2, is a transistor Tri.
and transistor Tr2 are connected in cascade to form an amplifier, and a resistor R1 is connected between the emitter of the transistor Tr2 and the base of the transistor Tri, and a resistor R2 is connected between the pace and ground of the transistor Tri. A resistor R3 is connected between the emitter and ground of the transistor Tri.
is connected, and the voltage across it is applied to the midpoint of variable resistor R4 via capacitor C3.

Variable resistor R4 is a resistor for varying the frequency,
Together with the resistor R5, it constitutes the emitter resistor of the transistor Tr2. Thus, resistance R1, capacitance 1ci, and resistance R
2. A bridge circuit is formed by the capacitance C2, the resistor R3, the resistor R4, and the capacitor CI, and the oscillation frequency is determined. The oscillation output of this oscillation circuit 2 is the detection circuit 3
The signal is transmitted to the amplification transistor Tr3 via a capacitor C4 and a resistor R6. The detection circuit 3 amplifies and detects the applied high frequency output, and has a smoothing circuit including capacitors C5 and C6 and a resistor R7.

FIG. 3 is a sectional view showing the structure of this water droplet detection sensor. In this embodiment, assuming that water droplets may adhere to the front surface of the glass plate 7, a water drop detection sensor is attached to the back surface of the glass plate 7. The water droplet detection sensor is housed inside a case 8 made of, for example, a synthetic resin material. The top plate of the case 8 constitutes the detection electrode plate 1 shown in FIG. 2, and the detection electrode 1a and the sub-electrode 1b surrounding the detection electrode 1a are formed on the back surface thereof, and the ground electrode IC is formed on the outer periphery thereof. Here, the ground electrode IC is formed integrally within the case 8 with a metal shield case 9 that encloses the oscillation circuit and the detection circuit section.

Next, FIG. 4 shows the characteristics of the output voltage change depending on the presence or absence of water adhering to the glass plate 7 with respect to the oscillation frequency of the oscillation circuit 2. In this figure, when a thin water film is uniformly attached to the surface of the glass plate 7, the amount of change in the output voltage corresponding to the frequency is shown by the illustrated curve A. On the other hand, when water droplets adhere to the glass plate 7, the amount of change in output voltage corresponding to the frequency is shown by straight line B in the figure. When using this water droplet detection sensor as a drive signal source for a vehicle's wiper, even if a thin film of water adheres to the glass plate 7 that serves as the window glass after the wiper is driven, the water film dries in an extremely short time. death,
There is no need to operate the wiper because the driver can fully grasp the situation ahead through the glass plate 7 and the water film. Therefore, at this time, it is not necessary to obtain a detection signal from the water droplet detection sensor, but if water droplets adhere to the glass plate 7, it is difficult to see what is ahead through the window glass, so it is necessary to operate the wiper promptly. Therefore, it is preferable that the amount of change in the output voltage due to the water film is as small as possible and the amount of change in the output voltage due to the water droplets is as large as possible. Therefore, the oscillation frequency of the oscillation circuit 2 should be set at least in a frequency band in which the amount of change in output voltage due to water droplets (straight line B) is larger than the amount of change in output voltage due to water film (curve A), and preferably in a frequency band where the difference is sufficiently large, that is, in the frequency band shown in FIG. As shown by the middle diagonal line, it is possible to detect only water droplets by setting the frequency band around I MHz as the starting wave number.

Next, the operation of this water droplet detection sensor will be explained with reference to the waveform diagram in FIG. Assume that the oscillation frequency is determined to be the frequency at which the difference between the curve A and the straight line B is the largest, for example, IMHz, by adjusting the circuit constants of the prefuge of the oscillation circuit 2. When power is supplied to this water drop detection sensor,
The oscillation circuit 2 oscillates at a predetermined frequency as shown in FIG. 5 ta+, which shows an AC waveform of the oscillation circuit 2. Since the oscillation frequency is selected at a frequency where the amplitude change due to the water film is small, at time t1
Even when a water film is deposited on the glass plate 7, the amplitude value hardly changes. However, if water droplets adhere to the glass plate 7 at time t2, the output of the detection circuit 3 decreases as shown in FIG.
3 collector voltage decreases. Therefore, it is possible to detect the presence or absence of water droplets based on this decrease in output.

Next, FIG. 6 is a circuit diagram showing an example of a wiper drive circuit using this water droplet detection sensor. As described above, the detection electrode plate 1 is connected to the oscillation circuit 2, and the oscillation output is given to the detection circuit 3 to constitute a water droplet detection sensor. The output of the water droplet detection sensor 10 is transmitted to an inverting amplifier 11 and amplified as shown in the figure. This amplified output eliminates fluctuations in the oscillation amplitude caused by long-term temperature changes in the oscillation circuit 2, detection circuit 3, and inverting amplifier 11, as well as long-term changes caused by dirt on the glass plate 7. The differential circuit 12 transmits only the short-term oscillation amplitude change caused by the adhesion of water droplets to the next stage comparator circuit 13. If a reference voltage is provided and the input signal exceeds this reference voltage, the detection output is transmitted to the wiper drive section 15.The wiper drive section 15 energizes the wiper 16 provided on the vehicle for a predetermined period of time based on the detection output. This causes the wiper 16 to operate.In this way, it becomes possible to control the wiper of the vehicle using the water droplet detection sensor 10.

Therefore, the user does not need to operate the wiper control switch one by one, and the wiper can be automatically driven according to the amount of raindrops.

In this embodiment, a sub-electrode 1b is provided around the detection electrode 1a to compensate for the temperature of the oscillation frequency, but in order to simplify the configuration, the sub-electrode may be omitted and used as the detection electrode plate. is also possible.

Furthermore, the water droplet detection sensor of the present invention can be applied not only to the wiper control of a vehicle but also to other devices.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a water droplet detection sensor according to the present invention, FIG. 2 is a top view showing an embodiment of a detection electrode plate used in this water droplet detection sensor, and FIG. 3 is a circuit diagram showing an embodiment of a water droplet detection sensor according to the present invention. A cross-sectional view showing the embodiment, Fig. 4 is a graph showing the oscillation frequency of the oscillation circuit used in the water droplet detection sensor and the amount of change in output voltage depending on the state of the water, and Fig. 5 shows the waveforms of various parts of this embodiment. The waveform diagram and FIG. 6 are block diagrams showing an example of the application of this water droplet detection sensor to a wiper drive circuit of a vehicle. 1--Detection electrode plate 1 a-----One detection electrode 1b--Sub electrode 1c--Ground electrode 2-----Oscillation circuit 3...-・−・
Detection circuit 7・−−1−−Glass plate 8・・・−・−
Case 9--Shield case 10--1-
-----Water drop detection sensor 11-Track 1 inverting amplifier circuit 1
2--------One differentiation circuit 13.--Comparison circuit
14--Setting device 15--Wiper drive section 16--Wiper Trl, Tr2
Transistor patent applicant Tateishi Electric Co., Ltd. agent Patent attorney Yoshiki Okamoto (and one other person) Figure 2 Figure 3 Figure 4 T! 'lE&f[Hz] Figure 5

Claims (3)

[Claims] (1) A sensing electrode plate having a sensing electrode and a ground electrode adjacent to the sensing electrode on an electrode surface, and the other surface serving as a sensing surface for detecting adhesion of water droplets, and static electricity between the electrodes of the sensing electrode plate. an oscillation circuit configured with a resonant circuit including a capacitance, and whose oscillation frequency is a frequency at which an amplitude change due to the presence or absence of water droplets on the detection surface of the detection electrode plate is larger than an amplitude change due to the presence or absence of a water film; and an oscillation amplitude of the oscillation circuit. A water droplet detection sensor, comprising: a detection circuit that detects a change, and detects adhesion of water droplets based on a change in capacitance of the detection electrode plate. (2) The oscillation circuit is characterized in that the oscillation frequency is set to a frequency at which the difference between the amplitude change due to the presence or absence of water droplets on the detection surface of the detection electrode plate and the amplitude change due to the presence or absence of a water film is sufficiently large. A water droplet detection sensor according to scope 1. (3) The water droplet detection sensor is attached to the back side of a window glass plate of a vehicle, and is connected to drive a wiper based on the detection circuit output. Water drop detection sensor described in section.