JPH02195250A - Apparatus for sensing rain drops for vehicle - Google Patents

Abstract

PURPOSE:To obtain a highly reliable apparatus free from influence of external radio waves and mechanical vibration by a method wherein piezoelectric device units for transmitting and receiving ultrasonic waves are attached adjacently on a window glass to detect rainfall based on fluctuation in reflected waves. CONSTITUTION:On an inner surface of a window glass 1, a piezoelectric device 21 for transmitting ultrasonic waves and a piezoelectric device 22 for receiving are attached adjacently. Transmitted wave 11 excited by a transmission circuit 3 of the device 21 is reflected on an outer surface of the glass 1 and received by the device 22. This constitution enables the device 22 to detect intensity of rainfall since reflected wave 13 fluctuates due to rain drops 12 when it rains. Then, via a receiving circuit 4, a wiper is controlled through a control unit 6.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method for automatically controlling the start and stop of a wiper provided on the window glass in front of the driver's seat of a vehicle such as an automobile. The present invention relates to a raindrop detection device for a vehicle that detects raindrops hitting glass.

[Conventional technology]

2. Description of the Related Art As passenger cars become more sophisticated, devices that automatically perform various operations have been developed and used.

If it rains while driving, the driver senses it and starts the wiper operation manually, but the system automatically detects raindrops hitting the windshield in front of the driver's seat and starts the wiper operation automatically. This method is also being put into practical use.

As a method for detecting WJ droplets hitting a window glass, for example, as shown in Japanese Utility Model Application No. 63-124656, a pair of electrodes as an antenna is attached to the window glass.
A method is known that detects changes in capacitance between electrodes due to raindrops coming into contact with window glass.

FIG. 3 is a conceptual diagram showing the antenna described above attached to the window glass of an automobile. The antenna 110 described above is attached to the window glass 1 in front of the driver's seat of the automobile 100. When raindrops hit the outer surface of the window glass l to which the antenna 110 is attached, the capacitance between the two electrodes constituting the antenna (not shown) changes at that moment. The presence or absence of raindrops is detected by converting this change into voltage, amplifying it as appropriate, and processing it.

In such a raindrop detection method, the antenna 110 receives external radio waves, which become noise and cause a decrease in detection sensitivity or malfunction of the detection device. In the device disclosed in the above-mentioned publication, the sensitivity of raindrop detection is improved by providing another antenna and using a differential amplifier to cancel out the external radio waves picked up by the two antennas.

(Problem to be Solved by the Invention) The method of detecting the presence or absence of raindrops from changes in capacitance between electric bridges has the drawback of being susceptible to external radio waves, so the device disclosed in the above-mentioned publication is adopted. Even if a method is adopted to eliminate this effect, there is a possibility that the external radio waves received by the two antennas may not be sufficiently eliminated due to aging of the semiconductor elements that make up the electronic circuit, including the differential amplifier.

SUMMARY OF THE INVENTION An object of the present invention is to provide a raindrop detection device for a vehicle that is free from a decrease in detection sensitivity or malfunction due to external factors such as external radio waves.

[Means to solve the problem]

In order to solve the above problems, the raindrop detection device for a vehicle of the present invention includes two piezoelectric element units for transmitting and receiving ultrasonic waves, which are attached adjacent to the inner surface of the window glass in front of the driver's seat of the vehicle; A transmitting circuit that generates a high-frequency voltage to be applied to a piezoelectric element unit for transmitting ultrasound waves, a receiving circuit that processes a received signal from the piezoelectric element unit for receiving ultrasonic waves, and an output signal of this receiving circuit as an input signal. It shall consist of a control unit that controls the

[Effect]

In the configuration of this invention, piezoelectric element units for ultrasonic transmission and ultrasonic reception are attached adjacent to each other on the inner surface of a window glass, and a high-frequency voltage is applied to the piezoelectric element unit for ultrasonic emission by a transmitting circuit. When it generates ultrasonic waves, when it is not raining, these ultrasonic waves are reflected off the outer surface of the window glass and are not scattered, so fewer reflected waves reach the piezoelectric element unit attached next to it for ultrasonic reception. When it is raining, when raindrops hit the outer surface of the window glass and adhere to it, the reflected waves are scattered and the number of reflected waves that reach the piezoelectric element unit for ultrasonic reception increases, and the frequency of these reflected waves is approximately equal to the frequency with which the raindrops hit. The amount of frequency fluctuation is proportional. Ultrasound is a high frequency wave at the MHz level, and the frequency range of the fluctuation component of the wave reflected by the raindrops mentioned above is from a few centimeters to a few hundred seconds above, so the piezoelectric element unit for ultrasonic reception receives this reflected wave and outputs it. The output signal is an amplitude modulated electrical signal. This electrical signal is processed by the receiving circuit and outputs the frequency of the increase or fluctuation of the reflected wave.Based on this output signal, the control unit can start, stop, intermittent operation, or reciprocate the wiper. Control is performed as necessary, such as by changing the cycle.Since the detected quantity is ultrasonic waves, there is no influence from external radio waves.Since the frequency of ultrasonic waves is at the M)tz level, the influence of mechanical vibrations generated by the vehicle is eliminated. I won't even receive it.

(Examples) The present invention will be described below based on Examples. FIG. 1 is a block diagram including a partial sectional view showing an embodiment of the present invention. In this figure, a piezoelectric element unit 21 for transmitting ultrasonic waves and a piezoelectric element unit 22 for receiving ultrasonic waves are attached adjacent to each other on the inner surface of a window glass 1. The piezoelectric element unit 21 is excited by the transmitting circuit 3 and emits an emitted wave 11 toward the window glass l. This ultrasonic wave as the transmitted wave 11 is almost 100% reflected by the outer surface of the window glass 1 and returns toward the piezoelectric element unit 21.

Since the emitted wave 11 does not have only a component perpendicular to the surface of the window glass 1, the emitted wave transmitted at an angle toward the receiving piezoelectric element unit 22 is reflected by the outer surface of the window glass 1, and then becomes piezoelectric. Although the figure shows one raindrop 12, there are no raindrops when it is not raining, so the piezoelectric element unit 22
The reflected wave received by is constant. It's raining and raindrops 1
2 hit and adhere to the window glass l one after another, each time a reflected wave 13 shown in the figure is generated and the amount of ultrasonic waves received by the piezoelectric element unit 22 temporarily increases.

By detecting changes in this reflected wave, it is possible to know when the rain has started or stopped, as well as the strength of the rain.

The receiving circuit 4 performs signal processing such as amplifying and detecting the electrical signal that the piezoelectric element unit 22 receives and converts into voltage, and is composed of an amplifier circuit 41, a detection circuit 42, and a low-pass filter 43. .

FIG. 2 is a waveform diagram for explaining the operation of the receiving circuit 4. The electrical signal 71 as the output signal of the amplifier circuit is obtained by linearly amplifying the electrical signal that the piezoelectric element unit 22 receives and converts the ultrasonic wave.The waveform in (a) is when it is not raining, and the piezoelectric element unit The amount of ultrasonic waves received by 22 is small and has a constant amplitude waveform with no fluctuations, (b)
The waveform is shown when it is raining, and as the ultrasonic waves are scattered by the raindrops 12, the amount of ultrasonic waves received by the piezoelectric element unit 22 increases and its amplitude changes, so the received signal 71 is distorted due to vibration. The waveform is as follows.

When this electric signal 71 is detected by the detection circuit 42, the electric signal 7 has a waveform in which the lower part of the electric signal 71 is cut off.
It becomes 2. While the frequency of ultrasonic waves is usually at the MHz level, the frequency of amplitude modulation by raindrops ranges from a few centimeters to several hundred meters at most. The electrical signal 72 contains a high frequency component whose fundamental frequency is twice the MHz level frequency of the ultrasonic wave, so it is received by cutting it with a low-pass filter 43 and passing it through a capacitor (not shown) to remove the DC component. An electrical signal 73 is obtained as the output signal of the circuit 4.

The frequency of this electrical signal 73 is proportional to the frequency with which raindrops 12 hit the window glass 1, as described above. The zero cross counter 5 is a circuit that detects the point in time when the input signal changes sign and adds up the number. The frequency of the electrical signal 73 can be determined by inputting the electrical signal 73 into the zero-cross counter 5 and adding up the number of changes in sign during a certain period. The required wiper control is performed by inputting an electric signal proportional to this frequency to the control unit 6. Although a conventional control unit 6 may be used, it is necessary to appropriately match the input signals. be.

The receiving circuit 4 has basically the same function as a radio receiving circuit, and the frequency of the ultrasonic wave corresponding to the carrier wave is MHz.
The receiving circuit 4 can be easily manufactured using conventional technology since the signal wave is in the medium wave to short wave range and the signal wave is in a slightly lower frequency range than that of voice.

The zero-cross counter 5 is often used as an electronic circuit suitable for determining the frequency of a relatively low-frequency electrical signal having an undefined amplitude, and is suitable for processing the electrical signal 73.

As the piezoelectric element units 21 and 22, commercially available piezoelectric ceramics, polymer piezoelectric elements, and the like can be used. Since a rectangular shape with sides of several centimeters to several centimeters can be easily obtained, the optimum dimensions can be set. In addition, since the front window glass of automobiles is usually curved, a polymer piezoelectric element is suitable as a piezoelectric element unit that adapts to the curved surface, and when using a piezoelectric ceramic, an adhesive It can also be used by filling the space between the window glass I and the piezoelectric element unit.

The dimensions and arrangement of the piezoelectric element units 21 and 22 are related to the thickness of the window glass 1 to which they are attached, but the conflicting requirements are that normal reflected waves are as small as possible and waves scattered by raindrops are efficiently received. Choose the one that best satisfies you.

In addition to the method of using the fluctuating component of the reflected wave as the output signal of the receiving circuit 4 as in the case of the electrical signal 73, it is also possible to extract the DC component of the electrical signal 72 and using this as the output signal of the receiving circuit 4. . As described above, when it rains, the amount of reflected waves received by the piezoelectric element unit 22 increases, so it is also possible to determine whether or not it is raining using this method.

〔Effect of the invention〕

As described above, this invention involves attaching piezoelectric element units for transmitting and receiving ultrasonic waves adjacent to each other on a window glass, and transmitting ultrasonic waves using the piezoelectric element unit for transmitting and receiving reflected waves. It is configured to receive with a piezoelectric element unit of The fluctuation component of the electrical signal as the output signal of the piezoelectric element unit is extracted and input to the control unit, and based on this input signal, the control unit controls the start, stop, intermittent operation, reciprocating cycle of wiper operation, etc. , Control is carried out as necessary.Since ultrasonic waves are used as the detection quantity, there is no influence from external radio waves.Since the frequency of ultrasonic waves is at the MHz level, it is not affected by mechanical vibrations generated by the vehicle. Furthermore, by using ultrasonic waves, it has become possible to construct a highly reliable raindrop detection device for vehicles.

[Brief explanation of the drawing]

Fig. 1 is a block diagram including a partial cross-sectional view showing an embodiment of the present invention, Fig. 2 is a waveform diagram for explaining the operation of the receiving circuit, and Fig. 3 is a detection of a raindrop detection device for a vehicle in the prior art. The installation of parts is a conceptual diagram of a car showing the position. DESCRIPTION OF SYMBOLS 1... Window glass, 21.22... Piezoelectric element unit, 3... Transmission circuit, 4... Receiving circuit, 6... Control unit. 2nd item 1st figure 30

Claims (1)

[Claims] 1) Two piezoelectric element units for transmitting and receiving ultrasonic waves attached adjacent to the inner surface of the window glass in front of the driver's seat of the vehicle, and a transmitter that generates a high-frequency voltage to be applied to the piezoelectric element unit for transmitting ultrasonic waves. A receiver circuit for a vehicle comprising a circuit, a receiver circuit that processes a received signal from the piezoelectric element unit for ultrasonic reception, and a control unit that performs necessary control using an output signal of the receiver circuit as an input signal. Raindrop detection device.