JPS61184448A - Waterdrop detection sensor - Google Patents

Abstract

PURPOSE:To prevent the sensitivity of a detection part from receiving the effect from the condition of a mount place or the change in temp., by grasping the detection of a waterdrop as the change in electrostatic capacity accompanied by the adhesion of the waterdrop. CONSTITUTION:The titled waterdrop detection sensor is used in automatically driving the wiper of a vehicle. When a waterdrop is adhered, the electrostatic capacity of a detection electrode part 1 changes and the oscillation amplitude of an oscillation circuit 2 changes. An integrator circuit 6 integrates the long- time output of the oscillation circuit 2 and this integrate output is imparted to the oscillation circuit 2 as an oscillation gain fixing control signal for keeping the oscillation gain of the oscillation circuit 2 constant. A first discriminator circuit 10 outputs a drive pulse to a control object when oscillation amplitude is equal to or more than a first reference value while a second discriminator circuit 14 forms a pulse signal when the oscillation amplitude is equal to or more than a second reference value smaller than the first reference value and outputs a drive pulse signal to the control object when the count value of said pulse value reached a predetermined value. A reset circuit 18 inputs said drive pulse signal to initialize the count of the second discriminator circuit 14.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a water droplet detection sensor used in cases such as detecting water droplets and automatically driving a controlled object such as a wiper of a vehicle. The present invention relates to a technique for responding to changes in the amount of water droplet adhesion and for distinguishing water droplet adhesion from disturbance vibrations (for example, vibrations caused by horns, etc.).

(Summary of the Invention) The present invention automatically adjusts the drive timing of the controlled object according to changes in the amount of attached water droplets while ensuring that the attachment of the water droplet detection electrode section is not affected by local conditions or temperature changes. It also makes it possible to detect water droplet adhesion more reliably by making it faster or slower, and by clearly distinguishing it from external vibrations.

(Prior art and its problems) Conventionally, a water drop detection sensor that detects rain drops and automatically drives the wiper of a vehicle has been used, for example, in "Nissan Giho" [December 1982 issue (No. 19)] Page 97 - 1st
02 page] is known.

Its composition is as follows.

That is, falling raindrops cause the diaphragm to vibrate, the piezoelectric element converts the vibration into voltage, and the voltage charges a charging circuit including a capacitor. When the charging voltage reaches the reference value, a wiper drive signal is output to drive the wiper. On the other hand, this wiper drive signal is input to the reset terminal of the charging circuit to instantly discharge the capacitor and stop the wiper drive once.

According to this conventional example, when the amount of rain is large and large raindrops collide with the diaphragm, the charging speed of the capacitor is fast and the wiper is immediately driven. In addition, when the amount of rain is low and small raindrops collide with the diaphragm, the charging speed of the capacitor is slow, and the wiper is not activated until multiple small raindrops collide within a predetermined time and the charging voltage reaches the reference value. drive

That is, the drive timing of the wiper is automatically advanced or delayed in accordance with changes in the size of raindrops.

However, the conventional example having such a configuration has the following problems.

(b) Disturbance vibrations other than vibrations caused by collisions with raindrops, especially small raindrops (for example, vibrations caused by the horns of own troops or other cars, vibrations of the vehicle body, etc.) cannot be distinguished from vibrations caused by collisions with raindrops, especially small raindrops. , there is a risk of causing a malfunction in the wiper drive.

(b) In order to solve the above-mentioned problem (a), the natural frequency of the diaphragm can be increased, but this requires increasing the rigidity of the diaphragm, which results in a decrease in sensitivity.

(c) A diaphragm and a piezoelectric element are used to pick up raindrops, but the apparent area of the diaphragm changes depending on the position and angle of installation on the vehicle body, and the impact energy of the raindrops changes accordingly. This affects the electromotive force of the piezoelectric element, making it difficult to distinguish between large particles and small particles, resulting in inaccurate wiper drive timing.

Since the diaphragm and the piezoelectric element increase the impact energy of raindrops, it is basically difficult to solve this problem.

(d) The sensitivity of the diaphragm and piezoelectric element fluctuates depending on temperature conditions, which can cause errors in wiper drive timing. In order to prevent this, a temperature compensation circuit is required, but this leads to a complicated circuit configuration and an increase in cost.

(Objective of the Invention) The present invention has been made in view of the above circumstances. Instead of detecting water droplets using vibrations caused by collision, the present invention detects water droplets by detecting them as changes in capacitance due to adhesion of water droplets. The sensitivity of the water droplet detection unit is installed so that it is not affected by local conditions or temperature changes, and automatically speeds up or slows down the drive timing of the controlled object according to changes in the amount of water droplet adhesion. The purpose of this invention is to improve the accuracy of the detection function, and to clarify the distinction between water droplet adhesion and external vibration without causing a decrease in sensitivity, thereby making it possible to reliably detect water droplet adhesion.

(Configuration and Effects of the Invention) In order to achieve the above object, the present invention has the following configuration.

That is, the water droplet detection sensor of the present invention includes: a detection electrode section that detects adhesion of water droplets by a change in capacitance; and a detection electrode section connected to the detection electrode section that varies the oscillation amplitude based on the change in capacitance; An oscillation circuit that varies the oscillation gain using an oscillation gain control input, and an oscillation gain fixing control signal that integrates the output of this oscillation circuit over a long period of time and uses the integrated output to maintain the oscillation gain of the oscillation circuit constant. a first discrimination circuit that inputs the output of the oscillation circuit and outputs a drive pulse signal to the controlled object when the oscillation amplitude is equal to or greater than a first reference value; input the output, and its oscillation amplitude is the first
Base? a second unit that generates a pulse signal when fJ, iiM or more is smaller than the $ value, counts this pulse signal, and outputs a drive pulse signal to the controlled object when the count value reaches a predetermined value; a discrimination circuit; and a drive pulse signal from the first discrimination circuit or the second discrimination circuit.
and a reset circuit that inputs a drive pulse signal from the discrimination circuit to initialize the count of the second discrimination circuit.

The effects of this configuration are as follows.

(i) When water droplets adhere to the sensing electrode directly or indirectly through glass, etc. (hereinafter simply referred to as adhesion, whether directly or indirectly), the capacitance of the sensing electrode changes, resulting in , the oscillation amplitude of the oscillation circuit is varied.

(2) Since the water droplets are large, when the first discrimination circuit determines that the oscillation amplitude of the oscillation circuit is equal to or greater than the first reference value, a drive pulse signal is immediately output to the controlled object to drive the controlled object.

Note that the counter is incremented by 1 in the second discrimination circuit as well, but the drive pulse signal from the first discrimination circuit is input to the reset circuit, which initializes the count of the second discrimination circuit and waits for the next water droplet to adhere.

■ When the water droplet is small, the first discrimination circuit does not output a drive pulse signal, but if the second discrimination circuit determines that the oscillation amplitude of the oscillation circuit is greater than or equal to the first reference value, the counter increases by +1. be done.

When small water droplets continue to adhere to the sensing electrode section, the counter is further incremented by one.

When the count value reaches a predetermined value in this manner, a drive pulse signal is output from the second discrimination circuit to the controlled object, thereby driving the controlled object.

The drive pulse signal is input to the reset circuit, initializes the count of the second discrimination circuit, and waits for water droplets to adhere to the second discrimination circuit.

In this way, when the water droplet adhering to the sensing electrode part is large, the control target is immediately driven, and when the water droplet adhering to the sensing electrode part is small, the number of times the water droplet adheres reaches a predetermined value. When the controlled object is driven for the first time.

That is, the drive timing of the controlled object is automatically accelerated or delayed in response to changes in the size of water droplets.

(11) The capacitance of the sensing electrode that picks up water droplets changes, but the capacitance also changes due to external vibrations such as vibrations caused by the horns of own troops or other cars, or vibrations of the vehicle body. .

However, in general, the change in capacitance due to such external vibrations is equal to or smaller than the change in capacitance due to the attachment of small water droplets. Further, disturbance vibration does not occur frequently.

Therefore, the first discrimination circuit does not operate depending on the disturbance vibration, and even if the second discrimination circuit counts, it usually ends only once or twice and does not reach the predetermined value, so the second discrimination circuit also outputs a drive pulse signal. do not.

In other words, since there is a clear distinction between water droplet adhesion and disturbance vibration,
The controlled object is driven only by the adhesion of water droplets, and is reliably prevented from being accidentally driven by external vibrations.

(Mountain) Elimination of the disturbance vibration in (ii) above is controlled by the count in the second discrimination circuit, and is not due to adjustment at the detection electrode section, which is pink-up, so the sensitivity of the detection electrode section decreases. Without this, the detection electrode section successfully detects the adhesion of water droplets as expected.

(1v) The integrating circuit integrates and outputs the output of the oscillating circuit over a long period of time, and the oscillating circuit maintains the oscillation gain constant based on the oscillation gain fixing control signal from the integrating circuit. Therefore, if there is no water droplet adhesion, such as during sunny weather, the oscillation gain fixing control signal is always output from the integrating circuit, and the oscillation gain of the oscillation circuit is automatically held constant.

That is, the mounting position and angle of the sensing electrode section are not affected by the mounting conditions, and the sensitivity of the sensing electrode section is always maintained constant.

(V) For the same reason as (iv) above, the sensitivity of the sensing electrode section is always maintained constant regardless of temperature conditions, even without providing a temperature compensation circuit or the like.

As described above, according to the present invention, the following effects are achieved.

+a) If the water droplets adhering to the sensing electrode are large, the controlled object is immediately driven; if the water droplets are small, the controlled object is driven only when the number of times the water droplets adhere reaches a predetermined value; It is possible to perform appropriate control by automatically speeding up or slowing down the drive timing of the controlled object in accordance with the change in the magnitude of.

fbl Since water droplet adhesion and disturbance vibration are clearly distinguished, the controlled object can be driven only by water droplet adhesion, and it is possible to reliably prevent accidental driving due to disturbance vibration.

Since this disturbance vibration is eliminated by the counting function of the second discrimination circuit, there is no need to reduce the sensitivity of the detection electrode section.
The adhesion of water droplets can be detected satisfactorily on the detection electrode portion as expected.

? '1(C) Since the oscillation circuit maintains the oscillation gain constant based on the integrated output over a long period of time, the sensitivity of the sensing electrode section is not affected by the mounting conditions or temperature conditions, and the oscillation gain is always kept constant. Water droplet adhesion can be detected with high sensitivity.

(Description of Examples) Hereinafter, the present invention will be described in detail based on examples shown in the drawings. FIG. 1 is a circuit diagram of a water droplet detection sensor according to an embodiment of the present invention.

<Circuit Description> The water droplet adhesion detection electrode section 1 is composed of a series circuit of capacitors C3 and C2. Although not shown, this series circuit actually consists of an elongated elliptical sensing electrode in the center, an annular sub-electrode surrounding it, and an annular grounding electrode surrounding this sub-electrode. and the sub-electrode constitute a capacitor C8, and the sub-electrode and the ground electrode constitute a capacitor C2.

In the case of a vehicle, the sensing electrode section 1 is usually attached to the inner surface of the windshield.

The oscillation circuit 2 includes transistors Tr+, Trz, resistors R, ~R1, etc., which are connected in series to form an amplifier circuit, a capacitor C1, and a field effect transistor (FET) 3.
It has

Each capacitor C+, Ci of the detection electrode section 1 is connected in parallel to a resistor R, , R, respectively, and a transistor Tr7. T
The collector of rz is connected to DC power supply Vcc. A series circuit of a capacitor C3 and a resistor R1 is connected between the emitters of the transistors Tr, Tr, and the emitter of the transistor Tr is grounded via the resistor R1. The emitter of the transistor Trz is connected via a resistor R0 to the base of the transistor Tr1 and the connection point between the capacitors C+ and Ct of the sensing electrode section 1, and the emitter of the transistor Trz
The base of r1 is grounded via resistor R2.

A connection point between the capacitor C3 and the resistor R4 is connected to the drain of the FET3 via the resistor R3, and the source of the FET3 is grounded via the resistor R6.

The oscillation frequency of the oscillation circuit 2 is set to 1 MIIz,
The %S detection circuit 4 includes a transistor Tr and a capacitor C1.
-C6, resistors Ry, Rs, etc., and an inverting amplifier circuit 5.

The capacitor C9 is connected to the emitter of the transistor Tr, which is the output terminal of the oscillation circuit 2, is grounded via the resistor R1, and is also connected to the base of the transistor Tr3. The collector of the transistor Tr is connected to a DC type fiVcc, and the emitter is grounded. The capacitor C3°C6 and the resistor R8 constitute a smoothing circuit whose input terminal is connected to the collector of the transistor Tr3 and whose output terminal is connected to the positive input terminal of the inverting amplifier circuit 5. The output terminal of the inverting amplifier circuit 5 is connected to the negative input terminal.

The integrating circuit 6 includes an operational amplifier 7 for integration, a capacitor C1, and resistors R7 to R11.

The output terminal of the inverting amplifier circuit 5 of the detection circuit 4 is connected to the negative input terminal of the operational amplifier 7 via a resistor R9, and is also connected to the output terminal of the operational amplifier 7 via a capacitor C7. The series circuit of resistors RIO+R1+ is connected to a DC power supply Vcc, and the connection point of resistors R1°+R++ is connected to the positive input terminal of the operational amplifier 7 to create its threshold.

The output terminal of the operational amplifier 7 is connected to the gate of the FET 3 of the oscillation circuit 2.

That is, the output of the detection circuit 4 is fed back to the oscillation circuit 2 via the integration circuit 6.

The amplifier circuit 8 includes an inverting amplifier circuit 9, a capacitor C8, and a resistor R32.

The capacitor C8 is connected to the output terminal of the inverting amplifier circuit 5 of the detection circuit 4, and is connected to the negative input terminal of the inverting amplifier circuit 9 via the resistor RI□. The positive input terminal of the inverting amplifier circuit 9 is connected to the DC type [Vcc] through a resistor R1° to create its threshold.

The first discrimination circuit 10 has a comparator 11 and a one-shot circuit 12. Resistance RIs + RI 41
The series circuit of RIS is connected to DC power supply Vcc to form a voltage dividing circuit.

The negative input terminal of the comparator 11 is connected to the output terminal of the inverting amplifier circuit 9, and the positive input terminal is connected to the resistor R1! .

It is connected to the connection point of RI4 to create its threshold, that is, the first reference value Vth+. An output terminal of the comparator 11 is connected to a one-shot circuit 12, and an output terminal of the one-shot circuit 12 is connected to an input terminal of a NAND gate 13.

The second discrimination circuit 14 includes a comparator 15 and a counter 1
6 and a one-shot circuit 17.

The negative input terminal of the comparator 15 is connected to the output terminal of the inverting amplifier circuit 9, and the positive input terminal is connected to the connection point of the resistor R94°RIS so that the threshold, that is, the second reference value v
I am making th. The output terminal of comparator 15 is connected to the input terminal of counter 16. counter 1
6 is composed of two flip-flops FF, FF2. The output terminal of the counter 16 is connected to a one-shot circuit 17, and the output terminal of the one-shot circuit 17 is connected to the input terminal of the NAND gate 13.

The output terminal of the NAND gate 13 is connected to the base of the switching transistor T r a of the wiper drive circuit, and is also connected to the counter reset circuit 18 .

The counter reset circuit 18 includes a one-shot circuit 19 connected to a DC power supply Vcc. The output terminal of this one-shot circuit 19 is connected to the positive terminal of each flip-flop FF, FF2 of the counter 16.

A clear circuit 20 clears and initializes the one-shot circuit 12 of the first discrimination circuit 10, the flip-flops FF, FFZ, and one-shot circuit 17 of the counter 16 in the second discrimination circuit 14 when the water droplet detection sensor is powered on. It is a circuit.

This clear circuit 20 is connected to the DC type 11 via a resistor R16.
It has a transistor Trs connected to 11JVcc, a capacitor C9, a Zener diode ZD, etc.

Note that 21 is a DC type @Vcc regulator.

<mh4^=i8H11> Next, the operation of this embodiment will be explained based on the time chart of FIG. 2.

(A) to (I) in FIG. 2 show the voltages at points a to i of the circuit of FIG. 1, respectively.

■ When the power is turned on, the resistor RI6 of the clear circuit 20 is connected to the DC power supply Vcc, and the one-shot circuit 12.1
7 and flip-flops FF, FF2 are cleared to the initial state. That is, the voltage e of the d output of the one-shot circuit 12 is "H" level, the voltage f of the Q output of the counter 16 is "L" level, and the voltage g of the d output of the one-shot circuit 17 is
becomes “H” level.

When capacitor C7 is charged and the charging voltage causes Zener diode ZD-t- to conduct, transistor Trs turns on and there is no clear output.

- When the power is turned on, the oscillation circuit 2 operates and starts oscillation. The voltage a at the output terminal of the detection circuit 4 maintains a constant oscillation amplitude in the absence of water droplets (period up to time t1).

Furthermore, when the power is turned on, a voltage is generated across the resistor R11 of the integrating circuit 6, which operates the operational amplifier 7 and outputs it to the gate of the FET 3. If the integrated output of the operational amplifier 7 is the result of integrating the output of the oscillation circuit 2 over a long period of time, that is, the output up to time (1), then it is proportional to the average oscillation amplitude of the oscillation circuit 2 during normal operation. This integrated output is applied to the gate of the FET 3, making the on-resistance of the FET 3 proportional to the integrated output and, in turn, to the oscillation amplitude of the oscillation circuit 2.

As a result, capacitor c3 and resistor R in oscillation circuit 2
The time constant determined by s, Rh, and the on-resistance of the FET 3 corresponds to the oscillation amplitude of the oscillation circuit 2.

Therefore, even if the oscillation amplitude changes from large to small due to the initial capacitance of the capacitors C,, C, differing depending on the conditions and temperature conditions, the mounting of the sensing electrode part 1 is not actually carried out as described above. Since the amplification gain of the transistor Tri, that is, the oscillation gain of the oscillation circuit 2 changes from small to large due to the change in the time constant of the oscillation circuit 2, the change in the oscillation amplitude is absorbed and the oscillation amplitude is always constant as long as there are no water droplets attached. maintain.

■When a large water droplet adheres to the sensing electrode part 1■ When one large water droplet adheres to the sensing electrode part 1 at time t1, the capacitance of the capacitors C, C2 changes, and as a result, the oscillation circuit The oscillation amplitude of 2 is varied.

The high frequency output from the oscillation circuit 2 with variable oscillation amplitude is detected, amplified and smoothed by the detection circuit 4, and the output voltage a of the inverting amplifier circuit 5 has a sinusoidal waveform as shown in FIG.

■ The output voltage a from the inverting amplifier circuit 5 is input to the negative input terminal of the operational amplifier 7 of the integrating circuit 6, but since the time constant is large, the output of the operational amplifier 7 does not change much, and the oscillation circuit 2 continues to oscillate. Ru.

Further, the output voltage a is input to the amplifier circuit 8, inverted and amplified by the inverting amplifier circuit 9, and outputs an output voltage having a sinusoidal waveform as shown in FIG.

■ This output voltage is input to the negative input terminal of the comparator 11 of the first discrimination circuit 10;
Since it is based on large water droplets, the first reference value vth,
be higher than Therefore, the comparator 11 is
As shown in the figure, the level is inverted from "H" level to "L" level.

This "L" level pulse signal is the one-shot circuit 12
and the output voltage is “L” as shown in figure (E).
``This becomes a level one-shot pulse signal e.

■ ``L'' level one-shot pulse (T No. 6 is N
It is input to AND gate 13. At this time, the voltage g of the output d of the one-shot circuit 17 is “
Since it is at H'' level, the NAND gate 13 becomes conductive, and the output voltage becomes H level as shown in FIG.

That is, in the case of large water droplets, the wiper is immediately driven by one water droplet.

■ The output voltage shown in FIG.
th, and the output voltage d of the comparator 15
is inverted from the "H" level to the "L" level as shown in Figure (D).

Then, the counter 16 counts +1, but the figure (H
The output voltage from the NAND gate 13 shown in ) is also input to the counter reset circuit 18, and as shown in FIG.

The counter 16 is reset to output to the reset terminal of FF2. Therefore, the output voltage f of the counter 16 is maintained at the "L" level as shown in FIG.

(2) Furthermore, since the reset pulse signal i is also output to the one-shot circuit 17 of the second discrimination circuit 14, the output voltage g of the one-shot circuit 17 maintains the "H" level as shown in FIG.

Since the reset pulse signal i is also output to the one-shot circuit 12 of the first discrimination circuit 10, the one-shot circuit 12
The voltage e of the d output returns to the "H" level as shown in Figure (E). As a result, the output voltage of the NAND gate 13 is inverted to the "L" level, the transistor Tra is turned off, and the wiper drive is stopped. That is, the wiper drive is 1
It is limited to one time only.

■When a small water droplet adheres to the sensing electrode part 1■ When one small water droplet adheres to the sensing electrode part 1 at time 1t, the capacitance of the capacitors C, C2 changes, causing the oscillation circuit 2 to oscillate. The amplitude is varied.

However, the amount of variation in the oscillation amplitude is small, and the amount of change in the output voltage a of the inverting amplifier circuit 5 is also small. Therefore, the amount of change in the output voltage S of the inverting amplifier circuit 9 of the amplifier circuit 8 is also small.

[Phase] This output voltage is input to the negative input terminal of the comparator 11 of the first discrimination circuit 10, but since this output voltage is based on small water droplets, the first reference value Vt
lower than h+. Therefore, the output voltage C of the comparator 11 is not inverted, and the voltage e of the output d of the one-shot circuit 12 is
is not reversed either.

■ The output voltage of the inverting amplifier circuit 9 is input to the negative input terminal of the comparator 15 of the second discrimination circuit 14, and this output voltage is higher than the second reference value Vthz.
The output voltage d of No. 5 is inverted from the "H" level to the "L" level as shown in FIG. 5(D).

Then, the counter 16 counts +1, but since it has not reached the predetermined value, the output voltage f of the counter 16 is not inverted, and the output voltage g of the one-shot circuit 17 is not inverted, so the output voltage of the NAND gate 13 is also maintains the "L" level. That is, the wiper drive circuit does not operate.

(2) When a second small water droplet adheres to the detection electrode section 1 at time L3, the output voltage f of the counter 16 becomes "H" level as shown in FIG. However, one-shot circuit 1
In order to maintain the voltage g of the d output of 7 at the “H” level, N
The output voltage of AND gate 13 is not inverted. That is, the wiper drive circuit does not operate.

When the third small water droplet adheres to the sensing electrode section 1 at time t4, the output voltage f of the counter 16 is reversed to the "L" level as shown in Figure CF), and the voltage of the output d of the one-shot circuit 17 is Since g is inverted to “L” level, NAN
The output voltage of the D gate 13 becomes "H" level, and the wiper drive circuit operates.

That is, the wiper is driven only when the third small water droplet is attached.

The output voltage from the NAND game) 13 is also input to the counter reset circuit 18, and at the rise of the output voltage, the reset pulse signal i is sent to the flip-flops FFl,
In order to output to the reset terminal of FFz, the counter 16 is loaded and waits for the next water droplet to adhere. Furthermore, since the one-shot circuit 17 is also reset, the wiper drive circuit stops.

That is, in this case as well, the wiper is driven only once.

[Brief Description of the Drawings] Fig. 1 is a circuit diagram of a water droplet detection sensor according to an embodiment of the present invention;
FIG. 2 is a time chart of voltages at various parts of the circuit. In the figure, reference numeral 1 indicates a detection electrode section, 2 an oscillation circuit, 6 an integration circuit, 10 a first discrimination circuit, 14 a second discrimination circuit, 16 a counter, and 18 a reset circuit.

Claims (1)

[Claims] (1) A detection electrode unit that detects adhesion of water droplets by a change in capacitance; and a detection electrode unit connected to the detection electrode unit to vary the oscillation amplitude based on the change in capacitance, and to adjust the oscillation gain by an oscillation gain control input. an oscillation circuit that varies the output of the oscillation circuit over a long period of time, and an integral output that is applied to the oscillation circuit as an oscillation gain fixing control signal for keeping the oscillation gain of the oscillation circuit constant. a first discrimination circuit that receives the output of the oscillation circuit and outputs a drive pulse signal to the controlled object when the oscillation amplitude is greater than or equal to a first reference value; The amplitude is the first
a second discrimination circuit that generates a pulse signal when the value is equal to or greater than a second reference value that is smaller than the reference value, counts the pulse signal, and outputs a drive pulse signal to the controlled object when the count value reaches a predetermined value; and a drive pulse signal from the first discrimination circuit or the second discrimination circuit.
A water droplet detection sensor comprising: a reset circuit that inputs a drive pulse signal from a discrimination circuit to initialize the count of the second discrimination circuit.