JP2007240186A - On-vehicle lane sensor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an on-vehicle rain sensor having excellent rainfall determination accuracy, capable of suppressing its decline especially caused by temperature fluctuation. <P>SOLUTION: Detection is performed by a rain detection PD 3 by using light reflected by a glass surface as detection light, by a reference light quantity detection PD 4 by using a part of light emitted from an LED 2 of the on-vehicle rain sensor as reference light, and a light quantity ratio which is a ratio between the detection light and the reference light is calculated (step S106). A relation between a temperature and the light quantity ratio at a clear time is learned (step S114), and rainfall is determined by the magnitude relation between the light quantity ratio at the present clear time determined from the present temperature and the learned relation, and the light quantity ratio calculated this time (step S110). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an in-vehicle rain sensor device that is mounted on a vehicle to detect and determine rainfall.

  Patent Document 1 proposes to correct the temperature characteristics of the in-vehicle rain sensor by changing the amplification gain of the signal voltage from the light receiving means in accordance with the change in ambient temperature.

  The following patent document 2 filed by the present applicant is based on a temperature characteristic indicating a relationship between a light-receiving element output of a vehicle-mounted rain sensor stored in advance and a temperature, and a current temperature detected by the temperature sensor. It has been proposed to suppress fluctuations in the light receiving element output due to temperature by correcting the output.

  When the above-described technique is used, it should be possible to solve the problem that the light receiving element output fluctuates depending on the temperature and the rain determination accuracy decreases. However, this presupposes that the temperature characteristics of the light receiving element outputs of the respective onboard rain sensors to be shipped are equal to each other. However, in reality, it is known that the temperature characteristic of the light receiving element output of each in-vehicle rain sensor has a non-negligible variation for each in-vehicle rain sensor.

Further, in Patent Document 1, when it is determined that there is no rain at the time of starting the engine, the temperature characteristic of the light receiving element output is obtained by storing the data pair of the light receiving element output (that is, the incident light amount of the light receiving unit) and the temperature. It also proposes to learn. Specifically, the light receiving element output (light during sunny day) is stored in memory at various temperatures, and the light during sunny day that matches the current temperature detected by the temperature sensor is read from the memory. The light amount and the current light receiving element output (detected light amount) are compared to make a rain judgment. Therefore, if this learning is performed ideally, the variation in the temperature characteristic of the light receiving element output for each in-vehicle rain sensor should be satisfactorily eliminated.
JP-A-11-326186 JP 2001-349961 A

  However, in order to compensate the temperature characteristics unique to the in-vehicle rain sensor with high accuracy, the light-receiving element outputs at various temperatures are obtained and the fine temperature characteristics are individually completed for each in-vehicle rain sensor. It is necessary to (learn). Therefore, when this learning is performed before shipment, it is not realistic because of large equipment and work load on the manufacturing side, and the above learning is completely completed with fine temperature divisions over a wide temperature range after shipment. Had the problem of requiring a long learning period.

  To explain more specifically about the case where the in-vehicle rain sensor is learned before shipping, the in-vehicle rain sensor is mounted on the glass surface for testing imitating the actual vehicle environment, and data is collected by changing various temperatures. The actual vehicle on which the in-vehicle rain sensor is mounted and the test glass surface have optical, thermal, and shape variations, and the state of the transparent buffer layer between the in-vehicle rain sensor and the glass surface is also present. Since they are different, the effect of temperature compensation by learning without using an actual vehicle is limited.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an in-vehicle rain sensor that can improve rainfall determination accuracy relatively quickly after shipment without imposing a great burden on the manufacturing side. It is said.

  A vehicle-mounted rain sensor according to a first aspect of the present invention for solving the above problems includes a light emitting unit that irradiates light on a glass surface of a vehicle, a temperature detecting unit that detects temperature, and detection light that is detected by reflection from the glass surface. Vehicle-mounted rain sensor comprising: a detection light detection unit that photoelectrically converts detection light that is the amount of light and outputs a detection signal corresponding to the detection light; and a signal processing unit that determines rainfall based on the detection signal and a detection temperature A reference light detection unit that photoelectrically converts reference light having a predetermined ratio of the light emission amount and outputs a reference signal corresponding to the reference light, and the signal processing unit amplifies the reference signal and the detection signal Amplifying unit, a light amount ratio calculating unit that calculates a light amount ratio that is a ratio of the detection signal to the reference signal, and a relationship between the sunny light amount ratio corresponding to the light amount ratio at the time of no rain and the temperature Memory and After reading the sunny light amount ratio corresponding to the temperature from the storage unit, the light amount ratio is compared with the sunny light amount ratio to determine whether there is rainfall, and the determination unit determines that there is no rain. A learning unit that learns the relationship by writing the detected temperature and the light amount ratio in the storage unit.

  That is, in this invention, a light emission part radiates | emits the reference light used as a fixed light quantity ratio with respect to the detection light irradiated to the glass surface which should detect rainfall to a predetermined | prescribed reference reflective surface. The reflected reference light is photoelectrically converted by the reference light detection unit to become a reference signal, and the reflected detection light is photoelectrically converted by the detection light detection unit to become a detection signal. Preferably, the reference reflecting surface should be placed as close as possible to the glass surface to reduce the difference in the optical path characteristics of both lights. Since the detected light amount is modulated by the raindrop adhering to the glass surface, the light amount ratio (detected light amount / reference light amount) decreases due to the raindrop adhering. Therefore, the rain determination can be performed by comparing the obtained light amount ratio with the sunny light amount ratio which is the rain determination threshold value. Hereinafter, this rain detection method is referred to as a light quantity ratio determination type rain detection method.

  According to this light quantity ratio determination type rain detection method, it is possible to remarkably improve the determination accuracy drop due to the temperature change of the rain detection unit. Hereinafter, the reason will be described. The change in the detected light amount due to the temperature change in the rain detection unit is caused by the change in the emitted light amount of the light emitting unit (usually LED) due to the temperature change and the change in the transmitted light amount of the optical path system due to the temperature change. Here, the transmitted light amount of the optical path system refers to the light amount that the light emitted from the light emitting unit enters the detection light detecting unit.

  When the amount of emitted light changes due to a temperature change, the reference amount of light also varies, so the light amount ratio is not affected by the temperature change of the light emitting unit. Therefore, if the rain determination is performed based on the light amount ratio, it is possible to cancel the temperature effect of the light emission amount of the light emitting unit and achieve excellent rain determination accuracy.

  The present invention further learns and corrects the fluctuation of the light amount ratio due to temperature change. As a result, it has been found that the accuracy of rainfall determination can be further improved. The reason for this will be described in detail. As described above, the light quantity ratio determination type rain detection method prevents the temperature effect on the light emitting unit. However, the influence of temperature change on the transmission characteristics of the optical path system cannot be canceled by this light quantity ratio determination method. On the contrary, in the light quantity ratio determination method, the temperature influence on the optical path system from the light emitting unit to the reference light detecting unit is taken into consideration. Therefore, a change in transmission characteristics of the optical path system due to a temperature change is very important. In view of this knowledge, the present invention learns the relationship between the temperature and the clear light amount ratio, detects the temperature, reads the clear light amount ratio corresponding to the detected temperature, and reads the clear light amount ratio and the detected light amount detected this time. And make a rain judgment. As a result, in addition to canceling the temperature effect on the light emitting unit by light quantity ratio determination, the influence of temperature change on the transmission efficiency fluctuation of the optical path system can also be canceled, so that it is possible to achieve much better rainfall determination accuracy than conventional ones. I was able to.

  In a preferred aspect, the signal processing unit learns the light amount ratio when it is determined that there is no rain in the initial rain determination, which is a rain determination operation for light amount ratio learning immediately after starting the vehicle, and thereafter the vehicle travels. The learning is also performed when it is determined that there is no rain in the normal rain determination, which is a rain determination operation that is sometimes performed.

  That is, compared with the conventional temperature characteristic learning type rain sensor that learns the amount of light when it is determined that there is no rain at the start of the vehicle as the amount of light during sunny days together with the temperature at that time, the temperature learning type in-vehicle rain sensor of this aspect is In addition to learning the light amount ratio and temperature when it is determined that there is no rain, the light amount ratio and temperature when it is determined that there is no rain during subsequent travel are learned.

  In this way, it becomes possible to acquire a detailed temperature-light quantity ratio relationship within a short period of time from vehicle shipment, and it is possible to make a precise rain determination at an early stage. In other words, since the temperature changes variously when the vehicle travels compared to when the vehicle is started in the rainless condition, a fine temperature-light quantity ratio relationship can be acquired in a short time. As a result, good determination accuracy can be reached early.

  In a preferred aspect, the signal processing unit feedback-controls the light emission amount of the light emitting unit so that at least the reference light amount falls within a predetermined range in the initial rain determination.

  That is, according to this aspect, when learning the light amount ratio immediately after starting the vehicle, even if the light emission amount of the light emitting unit fluctuates due to, for example, a temperature change or the like, the reference light with a certain optimal light amount enters the reference light detection unit. Therefore, the reference light equivalent voltage and the detection light equivalent voltage output from the amplifying unit can be set to an optimum magnitude, and the stability of the amplification factor can be improved. As a result, it is possible to improve the rain determination accuracy.

  In a preferred aspect, the signal processing unit sets the light emission amount of the light emitting unit to be greater than the light emission amount of the light emitting unit in the initial rain determination so that the detected light amount is suitable for rain determination in the normal rain determination. Feedback control is also performed. As a result, the amount of detected light can be set to an optimum level for normal rain determination.

  A vehicle-mounted rain sensor according to a second aspect of the present invention that solves the above-described problem is a photoelectric conversion of a light-emitting unit that irradiates light onto a glass surface of a vehicle and detection light that is the amount of detection light that is detected by reflection from the glass surface. In an in-vehicle rain sensor including a detection light detection unit that outputs a detection signal corresponding to the detection light and a signal processing unit that determines rainfall based on the detection signal, a reference light having a predetermined ratio of the light emission amount is photoelectrically detected. A reference light detection unit that converts and outputs a reference signal corresponding to the reference light; and the signal processing unit includes an amplification unit that amplifies the reference signal and the detection signal, and a ratio of the detection signal to the reference signal. A light amount ratio calculating unit that calculates a certain light amount ratio, and a determination unit that determines whether there is rainfall by comparing the light amount ratio with a predetermined sunny light amount ratio that is the light amount ratio at the time of no rain determination, The amplification unit is configured to detect the detection signal. Is output with a gain larger than that of the reference signal, and the detection signal is shifted by a predetermined offset amount so that the output voltage of the detection signal at the time of no rain detection is output within the output dynamic range of the amplification unit. It is characterized by doing.

  In the present invention, since the rain determination for learning the light amount ratio described above is performed, it is possible to improve the rain determination accuracy by canceling the influence of the variation in the light emission amount of the light emitting unit due to the temperature change.

  Moreover, the present invention amplifies the detection signal amplification (corresponding to the detection light) and the reference signal (corresponding to the reference light) from the reference light detection unit when the detection signal is amplified (also referred to as detection light gain). ) Is set larger than the gain in reference signal amplification (also referred to as reference optical gain), and further, an offset is applied in the direction of decreasing the detection signal output voltage so that the detection signal output voltage falls within the output dynamic range of the amplifier. adopt. The output dynamic range of the amplifying unit referred to here is a range between the minimum value and the maximum value of the output voltage of the amplifying unit. In this way, raindrop determination accuracy can be improved. Hereinafter, this point will be described in more detail.

  In order to increase the accuracy of raindrop determination, it is preferable to increase the amount of change in the detection signal due to the amount of raindrops adhering to the glass surface, that is, the amount of change in the output voltage of the amplifier. For this purpose, the gain of the amplifier is increased. There is a need. However, an increase in gain of the amplifying unit causes an increase in output voltage of the amplifying unit, and an amplifying unit having a very large output dynamic range is required. The output dynamic range of the amplifying unit has a predetermined limit depending on the power supply voltage value of the amplifying unit and the like, and it is difficult to produce an unlimited increase in the output dynamic range.

  Therefore, in the present invention, the gain for the detection signal is increased, and a necessary amount of offset is given to the output voltage of the amplifying unit, so that the output voltage corresponding to the amount of light during sunny day falls within this output dynamic range. Thereby, high raindrop detection sensitivity can be obtained within the output dynamic range of the amplifying unit.

  Furthermore, in the present invention, the amplifying unit performs amplification with a relatively small gain with respect to the reference signal. As a result, the output offset voltage range as given to the detection signal does not occur with respect to the reference signal. Therefore, even if the reference light amount is made smaller than the detection light amount at the time of fine weather, an output voltage corresponding to the reference signal can be output. For this reason, it is not necessary to increase the light emission amount of the light emitting unit in order to increase the reference light amount, and it is possible to prevent an increase in heat generation and temperature increase due to the increase in the reference light amount, thereby reducing fluctuations in the emitted light amount.

  In a preferred aspect, the amplifying unit outputs an output voltage of a reference signal within an output dynamic range range of the amplifier in an input voltage range in which the output voltage of the detection signal is substantially zero. Thereby, the reference light amount can be reduced while increasing the detection signal sensitivity.

  In a preferred aspect, the amplifying unit includes a common amplifying circuit having a gain switching circuit capable of switching a gain and an offset switching circuit capable of switching an offset amount, and the gain switching circuit includes a detection signal amplification period. The gain is increased by a predetermined ratio, and the output voltage is decreased by the offset amount. Thereby, the circuit configuration of the amplifying unit can be simplified.

  Preferred embodiments of the present invention will be described by the following embodiments. However, the present invention should not be construed as being limited to the following embodiments, and it goes without saying that the technical idea of the present invention may be implemented in combination with other techniques.

(Circuit configuration)
The circuit configuration will be described with reference to FIG. FIG. 1 is a block circuit diagram showing a circuit configuration of a rain sensor of this embodiment mounted on a vehicle. This rain sensor is a reflected light amount determination type rain sensor that determines rainfall based on a change in reflected light amount from raindrops attached to a glass surface of a vehicle or the like.

  In FIG. 1, 1 is an LED drive circuit, 2 is an LED, 3 is a rain detection PD, and 4 is a reference light quantity detection PD. As is well known, LED here refers to a light emitting diode and PD refers to a photodiode. It is naturally possible to replace the LED with another known electro-optic conversion element, or to replace the PD with another known photoelectric conversion element such as a phototransistor.

  Reference numeral 5 denotes a changeover switch for switching between the rain detection PD3 and the reference light quantity detection PD4, which is realized by an analog multiplexer circuit. This analog multiplexer circuit can be easily realized by using two CMOS transfer switches, for example, by turning on one and turning off the other, but it can also be easily applied to a bipolar transistor circuit such as a common emitter-connected differential circuit. Can be realized. The change-over switch 5 selects either the output signal of the rain detection PD 3 or the output signal of the reference light amount detection PD 4 and inputs the selected signal to the amplifier 6 described later.

  Reference numeral 6 denotes an amplifier that amplifies the voltage of the input signal from the rain detection PD 3 or the reference light amount detection PD 4 through the changeover switch 5, and it is natural that the amplifier 6 performs necessary power amplification in addition to voltage amplification. The amplifier 6 is preferably composed of a normal operational amplifier voltage amplifier circuit. Preferably, the output signals of the rain detection PD 3 and the reference light amount detection PD 4 are photocurrents proportional to the received light amount, and these photocurrents are signal voltages due to a voltage drop due to the input resistance of the amplifier 6 through the changeover switch 5. Is converted to Other types of operational amplifier circuits may be employed. The amplifier 6 has a function of switching the gain G by an external gain switching command and a function of switching an input offset voltage (also simply referred to as an offset) by an external offset switching command. For example, the gain switching of the operational amplifier voltage amplification circuit can be performed by switching the input resistance or the feedback resistance, and the offset switching can also be performed by switching the offset voltage input to the + input terminal. Since the switching of the gain and offset of the operational amplifier voltage amplification circuit itself is a conventional technique, further explanation is omitted.

  Reference numeral 7 denotes a temperature detection circuit, for example, a temperature sensor mounted on a circuit board. The temperature detection circuit 7 outputs an output voltage that changes substantially linearly with respect to temperature in the operating temperature range. This type of temperature detection circuit 7 is widely used, for example, as a thermistor type temperature sensor mounted on a circuit board.

  Reference numeral 8 denotes a CPU that constitutes a microcomputer together with the EEPROM 9. The CPU 8 performs a rain detection operation including a learning operation routine for rain determination and a rain determination routine operation based on the learning result based on a program stored in the EEPROM 9 or a memory area within itself. In the learning operation routine, the CPU 8 performs learning based on the temperature signal input from the temperature detection circuit 7 and the output voltage from the amplifier 6. Details of this learning operation will be described later. Reference numeral 10 denotes an A / D converter that converts the output voltage of the amplifier 6 into a digital signal and inputs the digital signal to the CPU 8.

(Modification)
In the above-described embodiment, the amplifier 6 is shared by switching the output signal of the rain detection PD 3 and the output signal of the reference light amount detection PD 4 at a constant interval by using the changeover switch 5. However, the present invention is not limited to this. Alternatively, an amplifier dedicated to the rain detection PD3 and an amplifier dedicated to the reference light quantity detection PD4 may be used in combination.

(Modification)
In order to remove disturbance light, the LED 2 may emit light at a predetermined frequency, and the amplifier 6 may have a band filter that passes a narrow band including this frequency. In this case, the gain and offset may be switched after detecting the signal voltage that has passed through the band filter, or they may be performed before the band filter.

  The basic operation of the rain sensor of FIG. 1 will be described below.

  The CPU 8 is activated when the ignition switch is turned on, and instructs the LED drive circuit 1 to emit light at a predetermined light emission amount. The LED drive circuit 1 causes the LED 2 to emit light at this light emission amount. This light emission amount is set so that the output signal voltage of the rain detection PD 3 output from the amplifier 6 becomes an optimum voltage (about 3 V) when the rain is normal under normal rain conditions.

  This rain sensor has a housing bonded and fixed to the inner surface of a vehicle windshield (not shown), and an LED 2, a rain detection PD 3, a reference light amount detection PD 4, and a prism are fixed to the housing. . The LED 2 irradiates infrared light obliquely toward the windshield through the prism. LED2 is arrange | positioned so that the infrared light to output may be totally reflected in the outer surface of a windshield. When raindrops adhere to the outer surface of the windshield, light is not totally reflected at the adhered portion but is transmitted to the outside, so that the detection light reflected by the windshield and incident on the rain detection PD 3 through the prism is reduced. The reference light quantity detection PD 4 is arranged at a position for receiving light reflected from a predetermined reflecting surface of the housing. Similarly, the infrared light emitted from the LED 2 is reflected by a predetermined reflecting surface of the prism and is incident on the reference light amount detection PD 4. Therefore, the output voltage of the reference light quantity detection PD 4 is not affected by rainfall at all.

  The rain detection PD 3 inputs a current (detection signal) corresponding to the incident light amount (detection light amount), and the reference light amount detection PD 4 inputs a current (reference signal) corresponding to the incident light amount (reference light amount) to the amplifier 6. Alternately amplifies these signals. The output voltage of the amplifier 6 is converted into a digital signal by the A / D converter 10 and input to the CPU 8.

  A preferred specific example of the rain detection operation will be specifically described with reference to the flowchart shown in FIG.

  First, the temperature is detected (S100), and the clear light amount ratio corresponding to the detected temperature is read from the EEPROM 9 (S102). Note that the EEPROM 9 is written with a basic temperature-clear light quantity ratio relationship at the time of shipment, and the clear light quantity ratio can be read immediately after shipment.

  In the next step S104, the gain of the amplifier with respect to the reference signal and the detection signal is switched to the initial light quantity ratio acquisition gain G1, and the output voltage of the amplifier 6 becomes a suitable value with respect to the reference signal and the sunny detection signal, respectively. The amount of light emitted from the LED 2 is feedback-controlled. In this embodiment, the light emission amount of the LED 2 is feedback-controlled so that an output voltage of about 1 to 4 V is output for both the reference signal and the sunny time detection signal. When it is difficult to control both the reference signal and the sunny detection signal within a suitable range with one type of gain, the gain of the amplifier 6 can be controlled in multiple stages, and the reference signal and the sunny detection signal It is also possible to control the gain independently. This type of LED feedback control itself is a well-known matter and will not be described in detail. Thereby, the output voltage of the amplifier 6 with respect to the detection signal and the output voltage with respect to the reference signal can be within the preferable output dynamic range of the amplifier 6. The preferable output dynamic range is also a preferable input dynamic range of the A / D converter 10 that converts the output voltage of the amplifier 6 into a digital signal.

(Modification)
In the above embodiment, the light emission amount of the LED 2 is feedback-controlled. However, an open control that gives a predetermined light emission amount command to the LED drive circuit 1 may be adopted so that the predetermined light emission amount is assumed.

  Next, the amplifier 6 outputs the output voltage for the detection signal and the output voltage for the reference signal through the A / D converter 10 (S106). Of course, at this time, the changeover switch 5 performs control to switch between the rain detection PD3 and the reference light quantity detection PD4.

  Next, from the output voltage for the detected signal and the output voltage for the reference signal, the amplifier characteristics are calculated back to calculate the input voltage to the amplifier, and the ratio of the input voltage, that is, the ratio of the detected light amount to the reference light amount The ratio is calculated (S108).

  Next, the calculated light amount ratio is compared with the sunny light amount ratio read in step S100 (S110). If the calculated light amount ratio is equal to or greater than the sunny light amount ratio, it is determined that there is no rain (S112). Using the relationship between the light quantity ratio and the temperature as new learning data, the temperature-light quantity ratio map is corrected (S114), and the corrected map is written into the EEPROM 9 (S116). In step S110, if the calculated light quantity ratio is less than the sunny light quantity ratio, it is determined that there is rain (S118), the wiper operation is commanded, and the process proceeds to step S120.

  That is, in steps S100 to S118, assuming that it is clear, a gain suitable for it is given to the amplifier 6 both when the reference signal is amplified and when the detection signal is amplified, and an appropriate light emission amount is given to the LED 2 to perform initial rain determination. The relationship between the temperature and the light quantity ratio is learned when it is determined that there is no rain.

  During the subsequent running, as described later, unlike the above, rain determination is performed under conditions optimal for rain determination (referred to as normal rain determination). This is because priority is given to the accuracy of normal rain determination. However, if it is determined that there is no rain even in this normal rain determination, learning of the relationship between the temperature and the light quantity ratio is performed to promote learning of the map. This normal rain determination control will be described in detail below.

  First, in step S120, the light emission amount of the LED 2 is feedback-controlled to an optimum light emission amount for normal rain determination described later. Further, the gain of the amplifier 6 is switched to the normal rain determination gain G2 so that the output voltage of the amplifier 6 becomes an optimum value (about 3 V in this embodiment) in the normal rain determination with respect to the light emission amount. At this time, an offset ΔV is applied to the amplifier 6 to adjust the output voltage of the amplifier 6 to a suitable range of A / D input, and the presence / absence of rainfall with high sensitivity is determined. More specifically, in this step S120, the output voltage of the amplifier 6 with respect to the detection signal input in the fine weather is the voltage range in which the amplifier 6 and the A / D converter 10 at the subsequent stage have the highest accuracy (here, around 3V). In addition, the light emission amount of the LED 2 is feedback-controlled so that the gain of the amplifier 6 with respect to the change of the detection signal becomes large. Note that simple switching control may be used instead of feedback control.

(Modification)
Also in this case, instead of feedback control, open control that gives a light emission command to the LED drive circuit 1 so as to emit this light emission amount may be adopted.

  In the next step S122, a detection signal is given from the rain detection PD 3 to the amplifier 6, an output voltage corresponding to this detection signal is given from the amplifier 6 to the CPU 8 through the A / D converter 10, and the output voltage input by the CPU 8 is obtained. A normal rain determination signal, which is a signal for determining normal rain, is created by using the normal rain determination signal. In this embodiment, the normal rain determination signal is a signal obtained by averaging the detected light amount detected by the rain detection PD 3.

  In the next step S124, the normal rain determination signal is compared with a normal rain determination threshold value stored in advance, and the detected light amount indicated by the normal rain determination signal corresponds to the normal rain determination threshold value. If it is less, it is determined that there is rain and a wiper operation is requested (S126). If the detected light quantity is equal to or greater than the threshold light quantity, it is determined that there is no rain and the process proceeds to step S128.

  Next, using the normal rain determination gain G2 and the offset ΔV, a detected light amount corresponding to a detection signal that is an output signal of the rain detection PD3 is read (S128).

  Next, the offset of the amplifier 6 is eliminated, the gain is switched to the reference light detection gain G3, the reference signal that is the output voltage of the reference light quantity detection PD4 is input to the amplifier 6, and the reference light quantity is read (S130). In addition, when calculating the reference light amount and the detected light amount, it goes without saying that the calculation is performed in consideration of the fact that the gain of the amplifier 6 is different.

  Next, a light amount ratio (detected light amount / reference light amount), which is a ratio between the detected detected light amount and the reference light amount, is calculated as a clear light amount ratio (S132), the temperature is read (S134), and the temperature and clear light amount ratio is read. The temperature-clear light quantity ratio map stored in the EEPROM 9 is corrected using the data pair (S136), the corrected map is written in the EEPROM 9 (S138), and the process returns to step S122.

(Explanation of gain setting)
In this embodiment, the gain G1 used at the time of acquiring the light amount data (S106) is equal to the gain G3 used in detecting the reference light amount for acquiring the light amount ratio after the normal rain determination. In addition, the gain G2 and the offset voltage ΔV used in the step (S122) of detecting the detected light amount for the above-described normal rain determination (S124) are used in the detected light amount detection for acquiring the light amount ratio after the normal rain determination. And the offset voltage ΔV. Thereby, the gain switching circuit and the offset switching circuit of the amplifier 6 can be simplified. Of course, if the number of gain switching stages and the number of offset switching stages are further increased, the gain sharing is not essential.

  FIG. 4 shows input / output characteristics of the amplifier 6 at the time of obtaining each light quantity. When the output voltage of the amplifier 6 corresponding to the amount of light detected during sunny weather is set to about 3V in the case of normal rain determination, the output voltage Vd corresponding to the detection signal decreased due to some raindrop adhesion is about 2 to 3V. Since the / D converter 10 uses a range where the SN ratio and linearity are high, the detection light quantity can be detected with high accuracy.

  The CPU 8 calculates the ratio (light quantity ratio), compares this ratio with a predetermined rain determination threshold value, and makes a rain determination. Thereby, the influence of the temperature change with respect to the emitted light amount of LED2 is canceled. However, the transmission efficiency of the reference optical path system and the rain detection optical path system fluctuates due to the influence of the temperature change, and the light amount ratio fluctuates due to the temperature change.

  Therefore, in this embodiment, in order to eliminate the temperature influence on the optical path system, the change characteristic of the light quantity ratio with respect to the temperature change is learned and used for the rain determination based on the light quantity ratio detected using this.

It is a block circuit diagram of the in-vehicle rain sensor of the present invention. It is a flowchart which shows the rain detection operation | movement of the vehicle-mounted rain sensor of FIG. It is a flowchart which shows the rain detection operation | movement of the vehicle-mounted rain sensor of FIG. It is a characteristic view which shows the input / output characteristic of the amplifier in each step.

Explanation of symbols

1 LED drive circuit (light emitting part)
2 LED (light emitting part)
3 PD for rain detection (detection light detector)
4 Reference light quantity detection PD (reference light detector)
5 changeover switch (signal processor)
6 Amplifier (Signal processing unit)
7 Temperature detection circuit (temperature detection unit)
8 CPU (signal processor)
9 EEPROM (storage unit)
10 A / D converter (signal processor)
Steps S108 and S132 (light quantity ratio calculation unit)
Step S110 (determination unit)
Steps S114 and S136 (learning unit)

Claims (7)

A light emitting unit for irradiating the glass surface of the vehicle with light;
A temperature detector for detecting the temperature;
A detection light detector that photoelectrically converts detection light that is the amount of detection light detected by reflection from the glass surface and outputs a detection signal corresponding to the detection light;
A signal processing unit for determining rainfall based on the detection signal and the detection temperature;
In-vehicle rain sensor comprising
A reference light detection unit that photoelectrically converts reference light having a predetermined ratio of the light emission amount and outputs a reference signal corresponding to the reference light;
The signal processing unit
An amplifier for amplifying the reference signal and the detection signal;
A light amount ratio calculating unit that calculates a light amount ratio that is a ratio of the detection signal to the reference signal;
A storage unit for storing a relationship between the light amount ratio in sunny time corresponding to the light amount ratio at the time of no rain determination and the temperature;
A determination unit that reads out the sunny light amount ratio corresponding to the detected temperature from the storage unit, and compares the light amount ratio with the sunny light amount ratio to determine whether there is rainfall;
A learning unit that writes the detected temperature and the light amount ratio in the storage unit and learns the relationship when the determination unit determines that there is no rain;
An in-vehicle rain sensor comprising: In-vehicle rain sensor according to claim 1,
The signal processing unit
Normal rain, which is a rain determination operation performed when the vehicle travels after learning the light ratio when it is determined that there is no rain in the initial rain determination, which is a rain determination operation for learning the light ratio immediately after the vehicle is started. An in-vehicle rain sensor that performs the learning even when it is determined that there is no rain. In-vehicle rain sensor according to claim 2,
The signal processing unit
An in-vehicle rain sensor that feedback-controls the light emission amount of the light emitting unit so that at least the reference light amount falls within a predetermined range in the initial rain determination. In-vehicle rain sensor according to claim 3,
The signal processing unit
An in-vehicle rain sensor that performs feedback control to increase the light emission amount of the light emitting unit to be larger than the light emission amount of the light emitting unit in the initial rain determination so that the detected light amount is suitable for rain determination in the normal rain determination. A light emitting unit for irradiating the glass surface of the vehicle with light;
A detection light detector that photoelectrically converts detection light that is the amount of detection light detected by reflection from the glass surface and outputs a detection signal corresponding to the detection light;
A signal processing unit for determining rainfall based on the detection signal;
In-vehicle rain sensor comprising
A reference light detection unit that photoelectrically converts reference light having a predetermined ratio of the light emission amount and outputs a reference signal corresponding to the reference light;
The signal processing unit
An amplifier for amplifying the reference signal and the detection signal;
A light amount ratio calculating unit that calculates a light amount ratio that is a ratio of the detection signal to the reference signal;
A determination unit that determines the presence or absence of rain by comparing the light amount ratio with a predetermined sunny light amount ratio that is the light amount ratio at the time of no rain determination;
Have
The amplification unit is
The detection signal is amplified with a gain larger than that of the reference signal, and the detection signal is shifted by a predetermined offset amount so that the output voltage of the detection signal at the time of no rain determination is within the output dynamic range of the amplification unit. An in-vehicle rain sensor characterized by In-vehicle rain sensor according to claim 5,
The amplification unit is
An in-vehicle rain sensor that outputs an output voltage of the detection signal at the time of rainless determination within a range of 35 to 65% of an output dynamic range of the amplification unit. In-vehicle rain sensor according to claim 5,
The amplification unit is
It consists of a common amplifier circuit having a gain switching circuit capable of switching the gain and an offset switching circuit capable of switching the offset amount,
The gain switching circuit is an in-vehicle rain sensor that increases the gain by a predetermined ratio and decreases the output voltage by the offset amount during a detection signal amplification period.

Images