JP3925442B2 - Rain sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rain sensor, and more particularly to an optical rain sensor that is attached to an inner surface of a vehicle windshield or the like and determines rain attached to an outer surface of the windshield or the like.
[0002]
[Prior art]
An optical rain sensor receives light from a light emitting source such as an LED from the inner surface side of the glass via a prism, reflects the light from the outer surface (outer interface) of the glass, and condenses the reflected light by the prism. Light is received by a photoelectric conversion element such as a diode. Further, since the detection signal of the photoelectric conversion element is a minute voltage, this detection voltage is amplified by the amplifier circuit, and the amplified output voltage is input to the arithmetic processing circuit. And after setting the output voltage of an amplifier circuit to the fixed value for A / D conversion, for example, 3.0V, rain determination is performed based on the fall amount (decrease rate) of the output voltage from this fixed value.
[0003]
The sensing performance of the sensor for raindrops is greatly affected by the area of light (detection area) irradiated on the outer surface (outer interface) of the glass. The larger the detection area, the greater the probability of raindrops. It becomes easier to detect.
[0004]
However, the enlargement of the detection area leads to an increase in the size of the sensor, and the mounting position of the sensor is inconvenient for the occupant because of the vicinity of the room mirror, and the cost of the sensor is increased.
[0005]
For this reason, adjustments are made so that a good rain determination can be made even with a small decrease rate by increasing the rain determination threshold in software, but the soft adjustment is also subject to the limitations of the resolution of the A / D converter, etc. There is a limit to the improvement in sensitivity, and good rain judgment is not possible.
[0006]
Therefore, the inventors of the present invention, prior to the present invention, for the purpose of providing a rain sensor capable of achieving both improvement in sensor sensitivity, size reduction, and cost reduction with a simple configuration, “detection of photoelectric conversion elements”. In a rain sensor that includes an amplifier circuit that amplifies the voltage and inputs it to the arithmetic processing circuit, and after setting the output voltage of the amplifier circuit to a constant value, performs rain determination based on the amount of decrease in the output voltage from the constant value An invention relating to a rain sensor (hereinafter referred to as a premise invention) characterized in that an amplifier circuit performs offset amplification has been filed as a patent application (Japanese Patent Application No. 2002-156918).
[0007]
This prerequisite invention will be specifically described in comparison with the prior art (a technique that does not perform offset amplification unlike the assumption invention). For example, as shown in FIG. 5, the amount of decrease in output voltage when the input voltage V2 of the amplifier circuit is 1.5 V and the output voltage V3 of the amplifier circuit is 3 V will be described. (1) In the prior art, FIG. As shown in the graph of (A), the amplifier amplification factor is doubled and the reference voltage can be adjusted to 3 V, and the rainfall is determined based on the output decrease from 3.0 V. When the output voltage drop amount is set to be twice as large as (1) using the offset amplification, the offset voltage is set to 3.0V and the reference voltage is set to 3V as shown in the graph of FIG. However, it is necessary to set the amplifier amplification factor to 4 times in order to adjust the output voltage. However, compared with the prior art (1), the output voltage drop is twice that of (1), so the sensor sensitivity is improved. be able to.
[0008]
[Problems to be solved by the invention]
However, it has been found that the base invention has the following problems. In other words, it has been found that the greater the amount of offset, the more saturated the output drop during heavy rainfall, making it impossible to detect rain and making accurate rain determination. More specifically, the case where the saturation of the output reduction amount occurs is when the raindrop having a large raindrop diameter hits the detection surface directly or when the detection area is reduced even if the rain amount is the same. .
[0009]
An object of the present invention is to provide a rain sensor that solves the problems of the premise invention as described above, and that can perform an accurate rain determination even during heavy rainfall with a simple configuration.
[0010]
[Means for Solving the Problems]
The rain sensor of the present invention includes an amplifier circuit that amplifies the detection voltage of the photoelectric conversion element and inputs the amplified voltage to the arithmetic processing circuit. After setting the output voltage of the amplifier circuit to a constant value, the output voltage from the constant value is reduced. In the rain sensor that performs rain determination based on the amount of decrease, and in which the amplifier circuit performs offset amplification, the arithmetic processing circuit determines whether or not the output voltage decrease amount is saturated and the output voltage decrease When the saturation of the quantity is determined, an instruction to reset the offset amplification of the amplifier circuit is given.
[0011]
According to the rain sensor of the present invention, when the output voltage decrease amount is not saturated, the amount of decrease from the constant value of the output voltage with respect to the same rainfall increases by offset amplification, so that the sensor sensitivity is improved, When the output voltage drop amount is saturated, such as during heavy rain, the output voltage drop amount does not increase by resetting offset amplification, making it possible to perform accurate rain determination.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a rain sensor according to an embodiment of the present invention will be described with reference to the drawings.
[0013]
1 is a conceptual system configuration diagram of a wiper control system using a rain sensor according to an embodiment, FIG. 2 is a circuit diagram of a rain sensor, FIG. 3 is a circuit diagram of an offset amplifier circuit in an amplifier circuit, and FIG. These show the flowchart showing the process which an arithmetic processing circuit performs, respectively.
[0014]
In FIG. 1, reference numeral 100 denotes a vehicle window, for example, a front window. A wiper 200 is disposed on the outer surface (front surface) 100a side of the window, and the wiper 200 is operated by a wiper motor (wiper driving device) 300, and performs an operation of wiping raindrops adhering to the window outer surface 100a during rain. A rain sensor 400 is installed on the inner surface (back surface) 100 b of the window 100. The rain sensor 400 is located at a position where it can detect the raindrop adhesion state in the area where the raindrops are wiped off by the wiper blade 500 on the outer surface 100a of the window, and is installed at a position that does not hinder the visibility. From the standpoint of, it is sufficiently downsized. A wiper switch 600 that is operated by an occupant is provided inside the vehicle. The wiper switch 600 includes at least an automatic instruction switch AUTO that instructs an automatic wiping mode in which the wiper 200 is automatically controlled based on the output of the rain sensor 400, a stop instruction switch OFF that instructs the wiper to stop, When the wiper 200 is manually operated, the wiper 200 has a low speed instruction switch LO for instructing a low speed wiping mode in which the wiper 200 operates at a low speed and a high speed instruction switch HI instructing a high speed wiping mode in which the wiper 200 operates at a high speed. The wiper motor 300, the rain sensor 400, and the wiper switch 600 are connected to the wiper drive circuit 700.
[0015]
In FIG. 2, the rain sensor 400 includes a light emitting unit 1, a light receiving unit 2, and a CPU (also referred to as a microcomputer or an arithmetic processing circuit) 3.
[0016]
The light emitting unit 1 includes one LED (light emission source) 11, and the light emission amount of the LED 11 can be adjusted by a current control transistor (light emission amount control element) 12. The light from the LED 11 enters from the inner surface 100b side of the glass 100 via a prism or the like, is reflected by the outer surface (outer interface) 100a of the glass 100, and the reflected light is condensed by the prism and is a photodiode (photoelectric conversion) of the light receiving unit 2. The device 21 receives the light.
[0017]
The light receiving unit 2 includes one photodiode 21, and the photodiode 21 receives the reflected light reflected by the glass outer surface 100a and generates a current proportional to the amount of received light. The light receiving section 2 is provided with an amplifier circuit 22, the amplifier circuit 22 inputs the current photodiode 21 is generated as the detection voltages V _1, the A / D port of CPU3 amplifies the detected voltages V ₁ input. The amplifier circuit 22 includes an amplifier circuit (not shown) in the previous stage (one or a plurality of stages) and an offset amplifier circuit 22A shown in FIG. 3 connected to the output terminal of the previous amplifier circuit. 3, the output voltage V ₂ of the preamplifier circuit is input to the non-inverting input terminal of the operational amplifier OA. A feedback resistor R ₂ is connected between the output terminal and the inverting input terminal, and the resistor R ₁ , the first semiconductor switch element SW 1, and the offset power source V ₀ are connected between the inverting input terminal and GND. series circuit of is connected, further, the second semiconductor switch element SW2 is connected in parallel with the first semiconductor switch element SW1 and the offset power source V _0. Therefore, the output voltage V ₃ of the operational amplifier OA is expressed by the following equation (1) when the first semiconductor switch element SW1 is in the off state and the second semiconductor switch element SW2 is in the on state, and is expressed by the offset amount (offset voltage). ) Becomes 0V, and when the first semiconductor switch element SW1 is in the on state and the second semiconductor switch element SW2 is in the off state, it is expressed by the following equation (2), and (R ₂ / R ₁ ) V ₀ is This is the offset amount (offset voltage). The output voltage V ₃ is input to the A / D port of the CPU 3. The first and second semiconductor switch elements SW1 and SW2 perform a switching operation according to a control signal from the CPU 3.
[0018]
V ₃ = (1 + R ₂ / R ₁ ) V ₂ (1)
V ₃ = (1 + R ₂ / R ₁ ) V ₂ − (R ₂ / R ₁ ) V ₀ (2)
Next, processing executed by the CPU 3 will be described with reference to FIG.
[0019]
When starting the processing, the CPU 3 instructs the amplifier circuit 22 to perform offset amplification in order to prioritize securing the field of view ahead of the vehicle, and sets the sensitivity of the sensor to be high, giving priority to wiping by the wiper 200. The semiconductor switch element SW1 is set to an on state, and the second semiconductor switch element SW2 is set to an off state.
[0020]
The CPU 3 determines whether or not the AUTO mode is selected (step S1), and performs the process at the time of low rainfall and heavy rainfall as described below only when the AUTO mode is selected.
[0021]
First, the CPU 3 performs AGC (automatic gain adjustment) so that the output voltage V ₃ becomes a constant value, for example, 3.0 V, the gain of the previous amplifier circuit of the amplifier circuit 22 and the base of the current control transistor 12 of the light emitting unit 1. The voltage is controlled (step S2).
[0022]
Next, the reference value, that is, the output signal (output voltage V ₃ ) of the operational amplifier OA when no raindrops are attached is taken in (step S3). For the reference value capture, the reference value stored in advance in the storage unit in the CPU 3 may be read out for the first time capture, or the wiper 200 is forcibly wiped once to wipe the reference value. the output voltage V ₃ of the immediately may be taken as a reference value. In the second and subsequent captures, the output voltage V ₃ immediately after wiping is captured.
[0023]
Next, the current output signal (output voltage V ₃ ) is captured (step S4). This capture timing is set when raindrops are attached to the window 100 after the wiper 200 performs the wiping operation.
[0024]
Next, rain determination is performed (step S5). In this rain determination, the ratio of the output voltage drop amount to the reference value, that is, the output voltage drop rate is calculated.
[0025]
Next, the wiping mode is selected from the output voltage drop rate (step S6). The wiping mode includes a stop mode in which the wiper 200 is not operated, and there are an intermittent mode, a low speed mode, and a high speed mode.
[0026]
Next, the wiper 200 is wiped according to the selected wiping mode (step S7).
[0027]
Next, it is determined whether or not the output decrease amount is saturated, in other words, whether or not the output voltage V ₃ is near 0 V (step S8).
[0028]
If it is determined that the output reduction amount is not saturated, the process returns to step S1, and the above-described processing is repeated until the AUTO mode is not selected.
[0029]
On the other hand, if it is determined that the output decrease amount is saturated, it is determined whether or not there is a splash determination (step S9). The splash determination is a determination made at the time of emergency wiping only a few times by splashing water or the like, and can be determined based on the output voltage drop rate or its temporal change.
[0030]
If there is a splash determination, that is, if it is determined that it is an emergency wiping time, the process returns to step S1.
[0031]
On the other hand, when there is no splash determination, that is, when it is determined that the emergency wiping is not performed, it is determined whether or not the AUTO mode is selected (step S10), and only when the AUTO mode is selected will be described below. Such heavy rain treatment is performed.
[0032]
First, the offset amount is set to 0V (step S11). That is, the first semiconductor switch element SW1 is switched off and the second semiconductor switch element SW2 is switched on, and the offset amplification is reset.
[0033]
Next, AGC (automatic gain adjustment) is performed, and the gain of the pre-stage amplifier circuit of the amplifier circuit 22 and the base voltage of the current control transistor 12 of the light emitting unit 1 are set so that the output voltage V ₃ becomes a constant value, for example, 3.0V. Control (step S12).
[0034]
Next, as in step S3, the reference value, that is, the output signal (output voltage V ₃ ) of the operational amplifier OA when no raindrops are attached is captured (step S13). This reference value is stored in advance in a storage unit in the CPU 3, and is read from this storage unit.
[0035]
Next, as in step S4, the current output signal (output voltage V ₃ ) is captured (step S14).
[0036]
Next, as in step S5, rain determination is performed (step S15).
[0037]
Next, similarly to step 6, the wiping mode is selected from the output voltage drop rate (step S16).
[0038]
Next, similarly to step S7, the wiper 200 is wiped according to the selected wiping mode (step S17).
[0039]
Next, it is determined whether or not the saturation of the output decrease amount has been canceled (step S18). The cancellation of the saturation of the output reduction amount is performed by setting a voltage value larger than the voltage value serving as a criterion for determining the saturation of the output reduction amount in step S8 in order to prevent hunting with the determination of the saturation of the output reduction amount in step S8. As a criterion for judgment, it has hysteresis characteristics.
[0040]
If it is determined that the saturation of the output reduction amount is not released, the process returns to step S10, and the processes of steps S11 to S18 are repeated until the AUTO mode is not selected.
[0041]
On the other hand, if it is determined that the saturation of the output decrease amount has been released, the process returns to step S1.
[0042]
As described above, the rain sensor 400 according to the present embodiment includes the amplification circuit 22 that amplifies the detection voltage V ₁ of the photoelectric conversion element (photodiode 21) and inputs the amplified voltage to the arithmetic processing circuit (CPU 3). A rain sensor for setting rain based on the amount of decrease in the output voltage V ₃ from the constant value 3.0V after setting the output voltage V ₃ of the circuit 22 to a constant value (for example, 3.0V). In the rain sensor that causes the circuit 22 to perform offset amplification, the arithmetic processing circuit 3 determines whether or not the output voltage decrease amount is saturated, and when determining that the output voltage decrease amount is saturated, the offset amplification of the amplifier circuit 22 is performed. Instructs to reset.
[0043]
According to the rain sensor 400 of the present embodiment, when the output voltage decrease amount is not saturated, the amount of decrease from the constant value 3.0 V of the output voltage V ₃ with respect to the same rainfall increases due to offset amplification, so that the sensor sensitivity is improved. In addition, when the output voltage drop amount is saturated, such as during heavy rainfall, the output voltage drop amount does not increase by resetting the offset amplification, and an accurate rain determination can be performed.
[0044]
【The invention's effect】
According to the present invention, an accurate rain determination can be performed with a simple configuration even during heavy rainfall.
[Brief description of the drawings]
FIG. 1 is a conceptual system configuration diagram of a wiper control system using a rain sensor according to an embodiment of the present invention.
FIG. 2 is a circuit diagram of a rain sensor.
FIG. 3 is a circuit diagram of an offset amplifier circuit in the amplifier circuit.
FIG. 4 is a flowchart showing processing performed by an arithmetic processing circuit.
FIG. 5 is an explanatory diagram of the function and effect of the base invention.
[Explanation of symbols]
400 Rain sensor 3 CPU (arithmetic processing circuit)
21 Photodiode (photoelectric conversion element)
22 amplifier circuit 22A offset amplifier circuit V ₁ detected voltage V ₃ output voltage

Claims (1)

Amplifying circuit that amplifies the detection voltage of the photoelectric conversion element and inputs it to the arithmetic processing circuit. After setting the output voltage of the amplifier circuit to a constant value, the rain determination is based on the amount of decrease in the output voltage from the constant value. In the rain sensor that performs the offset amplification in the amplification circuit,
The arithmetic processing circuit determines whether or not the output voltage drop amount is saturated, and instructs to reset the offset amplification of the amplifier circuit when the output voltage drop amount is saturated. Rain sensor to do.

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