JPH10338102A - Mirror device with heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mirror device with a heater of inexpensive constitution that can eliminate rain drops or frost by heating a mirror base only by an electric current without temperature control while preventing lowering of the reflecting performance of a reflecting film and impairing the clearing performance of the reflecting film. SOLUTION: This mirror device with a heater is provided with at least two mirrors 6, 7 with heaters of such structure that electrodes are formed at reflecting films 9 provided at the back faces of mirror bases and that a current is applied to the reflecting films 9 through the electrodes to provide the reflecting films 9 with the function of heating resistors so as to heat the mirror bases. The respective heating resistors 9 are series-connected and connected to a power supply 15 through a current control switch 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mirror with a heater which can remove water droplets, raindrops, dewdrops, icing and fogging of a mirror by heating the mirror substrate. More particularly, the present invention relates to a mirror device with a heater that can be used for a vehicle and can provide a suitable rear view to a driver and a passenger.

[0002]

2. Description of the Related Art Conventionally, when a vehicle is running during rainfall or snowfall in a cold region, water droplets adhere to a rearview mirror or the like, or the rearview mirror or the like freezes, thereby lowering the rear visibility of the rearview mirror. However, in view of the fact that safe driving may be hindered, a mirror with a heater that removes water droplets and iced matter attached to the surface of the mirror substrate by heating the mirror substrate has been proposed.

For example, Japanese Patent Application Laid-Open No. Hei 7-277152 discloses that an electrode is formed on a reflection film provided on the back surface of a mirror substrate, and a current is applied to the reflection film via the electrode, whereby a heating resistor is formed on the reflection film. A mirror with a heater that has the function of heating the mirror substrate to remove water droplets and frozen matter attached to the surface of the mirror substrate and controlling the heating temperature of the mirror substrate with a temperature detector such as a thermostat Is disclosed. According to this configuration, it is possible to prevent the mirror substrate from cracking due to excessive heating of the surface of the mirror substrate by the temperature detector, and to prevent burns due to contact of the human body with the mirror substrate.

In a vehicle, these mirrors with heaters are provided in a pair on the left and right sides of the vehicle, as shown in FIG. 5, and each reflection film (heat generating resistor) of the mirrors 1 and 2 with a heater has a harness 3. Is connected in parallel to a battery 5 as a DC power supply via a switch 4 for energization control.

[0005]

The conventional mirror with a heater has a structure in which the temperature of the surface of the mirror substrate is controlled by using a temperature detector such as a thermostat, so that the number of parts is large and the cost is high. There is a problem,
As a passive measure, a configuration that does not perform temperature control, that is, it is conceivable to not use a temperature detector such as a thermostat, but in such a passive measure, if the temperature of the mirror substrate rises excessively, As mentioned above,
There is a possibility that the mirror substrate may be cracked or burned due to contact of the human body with the mirror substrate. In order to prevent the temperature of the mirror substrate from excessively increasing, it is conceivable to reduce the current flowing through the heating resistor as much as possible. (Sunny rate) is reduced. That is, there is a problem that it is not possible to improve the sunny rate in a short time.

However, in consideration of the relationship between the improvement in the fineness ratio and the cost, it is desirable to reduce the cost as long as the reduction in the fineness ratio is not substantially affected even if it is sacrificed somewhat. Then, the inventor conducted the following experiment.

Table 1 below shows that the inventor has set a constant current of 15
This is experimental data obtained by measuring the maximum temperature of the mirror substrate, the defrosting performance (also referred to as dew-removing performance), and the sheet resistance value of the heating resistor when the mirror substrate is energized for one minute.

[0008]

[Table 1] As is evident from Table 1, the defrosting performance of the mirror (substituting for the clearing rate) becomes longer when the energizing current is reduced,
If the defrosting is performed in a range from 3.5 minutes to 5.5 minutes, it is considered that the decrease in the clearing rate is not substantially affected.

Therefore, as shown in Table 1, a constant current is supplied to the mirror with a heater to reduce the surface temperature of the mirror substrate to 80 degrees.
It is determined that it is desirable to set the energizing current between 0.43 A (ampere) and 0.75 A in order to set the temperature to the degree C or less.

For example, Table 2 below shows that the battery 5
3 shows the maximum temperature, the defrosting performance, and the sheet resistance when the voltage is set to 13.5 V (volt) and the energizing current is set to 0.6 A. The heating resistor (reflection film) at this time
Had a thickness of 180 Å.

[0011]

[Table 2] Next, a comparison was made of the defrosting performance of a mirror with a heater when temperature control was performed using a temperature detector such as a thermostat, and a mirror with a heater that was only energized without performing temperature control.

FIG. 3 is a graph showing the time change of the clearing rate over the entire surface of the mirror when defrosting. In FIG. 3, reference numerals A and B denote the time elapsed when the voltage of the battery 5 was set to 13.5 V, the energizing current was set to 3.7 A and 2.0 A, respectively, and the temperature was controlled by the thermostat. A line graph is shown, and a performance of a fineness of 100% within 3 minutes from the start of energization (a fineness of 80% or more in less than 2 minutes) is obtained. On the other hand, the symbols C and D set the voltage of the battery 5 to 13.5 V, set the energizing current constant without performing temperature control,
A line graph with respect to the passage of time when 0.75 A is set (see Table 1) is shown, and the clearing rate does not reach 100% even after 6 minutes from the start of energization (however, the clearing rate is less than 5 minutes). It reaches 95% after 6 minutes at 80% or more). Symbol E indicates that the voltage of the battery 5 is 13.5.
V shows a line graph with respect to the passage of time when the energizing current is set to 0.6 A without performing temperature control and the temperature is not controlled. Is in a range that does not substantially affect the decrease in the sunny rate, and therefore, the energizing current is set to 0.1.
It is conceivable that the mirror substrate is heated only by the supplied current without setting the temperature to 6 A and controlling the temperature. At this time, the thickness of the heating resistor is 180 Å as described above, and there is a predetermined relationship between the thickness of the heating resistor and the sheet resistance.

However, the heat generating resistor also functions as a reflection film, and if its thickness is too thin, its reflection performance deteriorates. FIG. 4 is a diagram showing the relationship between the reflectance of the heating resistor (reflection film), the sheet resistance value, and the film thickness, and the symbol a (dashed line) indicates the relationship between the sheet resistance value and the film thickness. The characteristic curve indicated by the reference numeral B (solid line) is a characteristic curve indicating the relationship between the reflectance and the film thickness. As indicated by the broken line a, the sheet resistance value increases exponentially as the film thickness decreases (exponentially decreases as the film thickness increases), while as indicated by the solid line B The reflectance is substantially constant when the film thickness is 200 Å or more, but tends to sharply decrease as the film thickness becomes thinner than 200 Å. Generally, when the film thickness is 370 Å or less, the appearance is excellent. When the thickness is less than 180 angstroms, in particular, when the thickness is less than 180 angstroms, a half mirror is formed so that the inside can be seen through. The range of the film thickness from 0 to 320 angstroms is usually thought as an unstable reflectance region, and the film thickness is more than 350 angstroms. , The reflectance is stable, but if the film thickness is too large, the reflection film becomes 1000 or more when glass is used for the mirror substrate. There is a risk of delamination when it comes to the mirror substrate.

On the other hand, the sheet resistance is stable at 500 Å or more. Therefore, in consideration of the reflectivity and the sheet resistance, the film thickness is desirably in the range of 500 Å to 1000 Å. From the viewpoint, it is difficult to heat the mirror substrate only by the energizing current without setting the energizing current to 0.6 A and performing temperature control.

In other words, when the voltage of the battery 5 is kept constant, the energizing current is set to 0.6 A, and the mirror substrate is heated only by the energizing current without performing temperature control, the sheet resistance value becomes 39 This is because the thickness of the reflective film must be set to about 180 angstroms in order to set it to 1 ohm / square, so that the reflective performance of the reflective film deteriorates. Then, the sheet resistance value becomes small, the supplied current becomes large, and the heat generation energy becomes too large.

The present invention has been made in view of the above circumstances, and has as its object to reduce the reflection performance of a reflective film as much as possible without deteriorating the reflective performance of the reflective film. It is an object of the present invention to provide an inexpensive mirror-equipped mirror device capable of heating a mirror substrate only by an energizing current without performing temperature control and removing raindrops, icing, and the like.

[0017]

According to the present invention, when one mirror with a heater is connected to a power supply (when each mirror with a heater is connected to a power supply in parallel), the voltage applied to the heating resistor is E, Assuming that the flowing current is I and the resistance is R, the thermal energy generated in the heating resistor by energization is
Since RI * I (= E * I), and when the sheet resistance is reduced by increasing the film thickness, the heat energy generated in the heating resistor increases, so it is difficult to increase the film thickness. In the case of a mirror having a pair of left and right sides, such as a mirror with a heater for a vehicle, these heating resistors having substantially the same sheet resistance value are connected in series and energized. For example, the voltage applied to each heating resistor becomes E / 2, and even if the current flowing through each heating resistor is doubled, the same thermal energy ((E / 2) * 2) as that of a single heating resistor is used.
I = E * I) can be generated, and the resistance R of the heat generating resistor can be reduced by that amount. The mirror device with a heater according to claim 1, In order to solve the above problem, an electrode is formed on a reflection film provided on the back surface of the mirror substrate, and a current is applied to the reflection film through the electrode to give the reflection film a function as a heating resistor. At least two or more mirrors with a heater configured to heat the mirror substrate are provided, and each of the heating resistors is connected in series and connected to a power source via a switch for controlling power supply.

According to a second aspect of the present invention, there is provided a mirror device with a heater according to the first aspect, wherein a sheet resistance value of the heating resistor is in a range of 5 to 15 ohm / square.

According to a third aspect of the present invention, there is provided a mirror device with a heater according to the first or second aspect, wherein the thickness of the heating resistor is in a range of 400 to 1000 Å. .

[0020]

According to the present invention, a heating resistor (reflection film) is connected in series. For example, two sheet heating resistors are connected in series to a battery (power supply). Assuming that R is equal, the voltage E applied to each heating resistor (reflection film) is 1/1 / B of the battery voltage.
When the current I flowing through the heating resistor (reflection film) is doubled, the heat energy generated by the current becomes E * I, which is the same as the heat energy generated in the case of one mirror with a heater. Therefore, the sheet resistance of each heating resistor can be reduced to 1/4 of that of one mirror with a heater, and the thickness of each heating resistor (reflection film) can be increased.

[0021]

1A shows an electric connection circuit of a mirror device with a heater according to the present invention, FIG. 1B shows an equivalent circuit thereof, and FIG. 2 shows an exploded perspective view of the mirror with a heater. FIG. In FIG. 1, reference numerals 6 and 7 denote door mirrors as mirrors with a heater. As shown in FIG. 2, each of the mirrors with heaters 6 and 7 has a metal reflection film 9 formed on the back surface of a glass substrate as a transparent mirror substrate 8 by means such as vapor deposition. A pair of electrodes 10 and 11 are formed on the reflection film 9 by a method such as printing, and harnesses 12 and 13 are connected to the electrodes 10 and 11.
The reflection film 9 plays a role as a heating resistor for heating the transparent mirror substrate 8 when energized. The respective reflection films 9 are connected in series, and are connected by harnesses 12 and 13 to a battery 15 serving as a DC power supply via a conduction control switch 14.

Here, the voltage E of the battery 15 is about 1
Assuming that the sheet resistance of each reflection film 9 is equal to 3.5 volts, the voltage applied to each reflection film 9 is
It is about 6.75 volts, and in order to obtain the same defrosting performance of 4.5 minutes as shown in Table 2, a current (1.2 A) twice as large as that of one piece is applied to each reflection film 9. Then, when a table corresponding to Table 2 is created, it becomes as shown in Table 3.

[0023]

[Table 3] As shown in Table 3, the characteristic curve of the clear ratio with respect to the passage of time when the current I is 1.2 A and the sheet resistance is 10.6 ohms / square is indicated by reference numerals in FIG. This figure 3
As can be seen from the sign, it is possible to obtain a substantially equal fine rate (the fine rate after 5 minutes from the start of energization is about 82%) as compared with the fine rate when the energizing current I is 0.6 A. Can,
At this time, the thickness of the reflection film 9 is 540 angstroms as is apparent from the graph shown in FIG.

In other words, if the current flowing by connecting the reflection films 9 in series is twice as large as that of a single case, the temperature control switch 14 is turned on and off, and the respective reflection films 9 are energized. 9 without deteriorating the reflectance performance of the reflection film 9 and without sacrificing the fineness performance of the reflection film 9 as much as possible.
An inexpensive configuration can be provided in which the transparent mirror substrate 8 can be heated only by the supplied current without temperature control to remove raindrops, icing, and the like.

The sheet resistance of the reflection film (heat generating resistor) 9 is preferably around 10 ohms / square, but is preferably 5 ohms / square.
If it is within the range of 15 ohms / square, it is possible to remove raindrops and icing only by applying electricity while preventing cracking of the mirror substrate 8 and burns caused by contact of the human body with the mirror substrate 8 without substantially sacrificing the sunny rate. It can be performed. Further, if the thickness of the reflection film 9 is in the range of 400 Å to 1000 Å, there is no problem in the reflection performance, and it is even better if it is in the range of 500 Å to 1000 Å.

[0026]

Since the mirror device with a heater according to the present invention is constructed as described above, it can be manufactured inexpensively, without deteriorating the reflection performance of the reflection film, and improving the fineness of the reflection film. Without sacrificing as much as possible, there is an effect that the mirror substrate can be heated only by the energizing current without performing temperature control to remove raindrops, icing and the like adhering to the mirror substrate, and the energizing current is also reduced to There is an effect that the number can be reduced as compared with a mirror with a heater that performs temperature control.

[Brief description of the drawings]

1A and 1B are diagrams showing an embodiment of a mirror device with a heater according to the present invention, wherein FIG. 1A is an explanatory diagram of an electric connection circuit of the mirror device with a heater, and FIG. The figure is shown.

FIG. 2 is an exploded perspective view of a mirror with a heater according to the present invention.

FIG. 3 is a line graph for explaining a change in a sunny ratio with respect to the entire surface of the mirror at the time of exposure.

FIG. 4 is a graph for explaining a relationship among a reflectance of a mirror substrate, a sheet resistance value, and a film thickness of a reflection film.

FIG. 5 is an explanatory diagram showing a general electric connection circuit of a mirror with a heater.

[Explanation of symbols]

 6, 7: Door mirror (mirror with heater) 8: Mirror substrate 9: Reflective film (heating resistor) 10, 11: Electrode 14: Switch for energization control 15: Power supply (battery)

Claims (3)

[Claims] An electrode is formed on a reflection film provided on a back surface of a mirror substrate, and a current is applied to the reflection film through the electrode to give the reflection film a function as a heating resistor, thereby providing the mirror substrate with a function. A mirror device with a heater, wherein at least two or more mirrors with a heater having a structure for heating the heater are provided, and each of the heating resistors is connected in series and connected to a power source via a switch for controlling power supply. 2. The mirror device with a heater according to claim 1, wherein a sheet resistance value of the heating resistor is in a range of 5 to 15 ohm / square. 3. The heating resistor has a thickness of 400 to 1
The mirror device with a heater according to claim 1 or 2, wherein the mirror device is within a range of 000 angstroms.