JPH048261B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a control device for an auto-dimming mirror for an automobile.

[Prior Art] Generally, a rearview mirror for a car is used to view the rear of the car, but when driving at night, when the light from the headlights of a following car directly enters the mirror, the driver feels dazzled. Therefore, conventionally, as shown in Fig. 1, an optical sensor 1 detects light from the rear of the car and amplifies it using an amplifier 3, and an optical sensor 2 detects the brightness of the surroundings (for example, around the windshield). The comparator 5 compares the outputs of the amplifiers 3 and 4, and when the light from the rear is stronger than the surrounding light, it is determined that the light from the headlights of the following vehicle has entered, and the driver's vehicle is reflected in the mirror 6. A current is passed through the electromagnet 7 to change the reflection surface of the mirror 6 so as to reduce the reflected light in the direction.

FIG. 2 shows another conventional example. In this example, a liquid crystal cell 8 is provided on the surface of a mirror 6, and an oscillator 9 is controlled by the output of a comparator 5. When the light from the rear is strong, the oscillator 9 is turned off. The output is applied to the liquid crystal cell 8 to lower its transmittance and reduce reflected light.

However, in the conventional device as described above, when the surroundings are dark at night and there is almost no light from the following vehicle, the optical sensors 1 and 2 generate outputs due to the dark current and the offset voltage of the amplifiers 3 and 4, and the light from behind is generated. Although the light was weak, the reflectance of the mirror 6 decreased, making it difficult to see behind. Also, in the daytime, the brightness is very bright, so amplifiers 3 and 4
The output of the comparator 5 becomes saturated, and the saturation voltages of amplifiers 3 and 4 are compared, making it unclear what the output of the comparator 5 will be, and the reflectance of the mirror 6 changes frequently. occurred. This can be prevented by interlocking the power supply of the control device with the lighting switch.
The above-mentioned problem occurred because the lights were turned on in case of rain or fog or at dusk.

[Summary of the invention]

The present invention has been accomplished in order to eliminate the above-mentioned conventional drawbacks. That is, the brightness at night is usually less than 10 lux, but under street lights, it exceeds 20 lux. Also, the brightness from behind is less than 10 lux, but when the lights of the car behind you hit it, the brightness increases to 20 to 30 lux. Therefore, it is desirable that at night the output voltage of the amplifier increases approximately in proportion to the intensity of light. Also, during the daytime, the brightness can reach up to several tens of thousands of luxes, but during rain, fog, or dusk, the brightness can range from several hundred to one thousand luxes. Therefore, if the amplifier has proportional characteristics, the output will be saturated at 200 to 300 lux, so it is better to give the amplifier logarithmic characteristics. Also, the brightness
In a dark place of 10 lux or less, the influence of the dark current of the photosensor and the offset voltage of the amplifier is large, so it is sufficient to clamp the output of the photosensor that detects the brightness behind. An object of the present invention is to ensure the operation of the comparator by using the above-mentioned means, and to prevent unnecessary decreases or changes in the reflectance of the mirror.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 3, the outputs of optical sensors 1 and 2 are amplified by current amplifiers 10 and 12, respectively, and are several hundred mV.
voltage. If this voltage is amplified as it is, it will become saturated, so negative feedback is applied via diodes 14 and 16 in the next stage amplifiers 11 and 13. Since the current-voltage characteristics of the diode can be expressed as an exponential function, the amplification characteristics of the amplifiers 11 and 13 become logarithmic due to the feedback of the current. Note that the resistors 15 and 17 are provided to prevent the outputs of the amplifiers 11 and 13 from completely reaching a ceiling due to logarithmic characteristics.

FIG. 4 shows the amplification characteristics of the amplifiers 11 and 13,
The voltage at which the output voltage suddenly reaches a ceiling is determined by the voltage and current characteristics of the diodes 14 and 16, but in a normal Si diode, the voltage across both ends is about 0.7V, so if you want to increase this voltage, connect multiple diodes in series. Just connect them individually.

In addition, when it is dark at night, the output voltage is small, and the output after amplification by the optical sensor 2 that detects the surrounding brightness is several tens to several hundreds of mV, and the output of the optical sensor 1 that detects light from behind. Similarly, the amplified output as it is will be several tens to hundreds of mV. However, in this state, no light is coming from the following vehicle, so the input of light from the rear to the comparator 5 must be reduced. In this embodiment, the transistor 18
This constitutes a clamp circuit. That is, when the output of the amplifier 11 is small and the voltage between the emitter and the base of the transistor 18 is lower than about 0.7V, the resistance between the emitter and the collector of the transistor 18 is sufficiently high so that almost no voltage appears on the output side. The output of the amplifier 11 increases to a certain extent, and the voltage between the emitter and base of the transistor 18 increases.
When the voltage exceeds 0.7V, the resistance between the emitter and collector decreases rapidly due to the amplification effect of the transistor 18.
Output voltage appears. Therefore, the output after amplification should be about 0.7V at a brightness of about 10 lux, which is the background brightness.

Therefore, the characteristic of output voltage with respect to brightness is the fifth
The result will be as shown in the figure. The output due to the ambient light, that is, the output of the amplifier 13 shown in FIG. 1 increases almost linearly from the offset output and begins to saturate at about 40 lux. The output of the transistor 18 due to light from the rear shown in FIG. 2 is zero until about 10 lux, then rises sharply, and begins to saturate at about 40 lux. The outputs shown in A and B are compared by a comparator 5, and the output of the comparator 5 controls a mirror 6 through the means shown in FIGS. 1 and 2.

〔Effect of the invention〕

As described above, in the present invention, the amplifier that amplifies the output of each optical sensor has a logarithmic amplification characteristic, so that the amplifier does not saturate even when it is relatively bright such as at dusk, and the reflectance of the mirror is does not change frequently. Furthermore, by clamping the output of the optical sensor that detects light from behind, the reflectance of the mirror does not decrease unnecessarily during dark nights.

[Brief explanation of drawings]

Figures 1 and 2 are block diagrams of conventional devices, respectively;
Figure 3 is a configuration diagram of the device of the present invention, Figures 4 and 5.
Each figure is a characteristic diagram of the device of the present invention. 1, 2... Optical sensor, 5... Comparator, 6... Mirror, 7... Electromagnet, 8... Liquid crystal cell, 9... Oscillator, 10, 12... Current amplifier, 11, 13...
...Amplifier, 14,16...Diode, 15,1
7...Resistor, 18...Transistor. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A first optical sensor that detects the brightness of light from behind the automobile, a second optical sensor that detects the ambient brightness, and outputs of the first and second optical sensors. a comparator that compares the output of each amplifier, and a comparator that amplifies the output of each amplifier and has logarithmic amplification characteristics;
1. A control device for an auto-dimming mirror for an automobile, comprising means for reducing the reflectance of the mirror toward a driver when the output is greater than the output of an amplifier. 2 A first optical sensor that detects the brightness of light from behind the car, a second optical sensor that detects the surrounding brightness, and amplifies the output of the first optical sensor with logarithmic amplification characteristics. and a first amplifier having a function of clamping the output of the first optical sensor to a set level, a second amplifier that amplifies the output of the second optical sensor with logarithmic amplification characteristics, and An auto-dimming mirror for an automobile, comprising a comparator for comparing outputs, and means for reducing the reflectance of the mirror toward a driver when the output of the first amplifier is greater than the output of the second amplifier. control device.