JPH0285042A - Heater-equipped glass - Google Patents

Abstract

PURPOSE:To prevent deterioration of a glass base board, in an arrangement where a heater film consisting of a clear electroconductive film is formed on a glass surface between current supply electrodes formed along two opposite edges of glass base board concerned, by effectively sensing temp. change on the glass surface caused by cracking. CONSTITUTION:In a glass base board 1 used to the wind shield of a car, band- shaped current supply electrodes 2, 3 are formed parallelly along the upper and lower edges of the glass mating surface, and a clear electroconductive film is formed on the glass surface between these two electrodes 2, 3 to accomplish a heater film 4. As a thermo-sensor, thermistors 6A, 6B are installed on the glass surface near one end 21 of the electrode 2 and on the glass surface near that end of electrode 3 farther than the current supply part, and they are connected with an alarm circuit 7. If cracking is generated in this glass base board 1, the current supply electrode 2 will sever to cause increase of the current density in the heater film 4 near one end 21 of the electrode 2. If thereby the temp. of glass surface in this part rises abruptly, an alarm indicator lamp is lighted, and current supply to the heater film 4 is stopped.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to glass with a heater, and in particular to effectively detecting temperature changes on the glass surface due to cracks in the glass to prevent deterioration of the glass substrate. Regarding glass with tags.

[Prior Art] The above-mentioned glass with a shield has a heater film made of a transparent conductive film and a current-carrying electrode formed on the glass surface, and ice on the glass surface is quickly melted by applying electricity to the heater film. In recent years, attempts have been made to use heated glass as windshield glass for vehicles.

By the way, the above-mentioned windshield glass may crack due to the collision of foreign objects, etc. If such cracks occur especially near the current-carrying electrode and the wire breaks, the current flowing through the heater membrane will be greatly biased, causing the glass to locally overheat. In this type of heater-equipped glass, which often uses laminated glass, there is a problem in that the durability of the glass substrate is significantly reduced due to the large difference in temperature distribution.

Therefore, methods for detecting cracks in glass with a heater have been proposed. For example, Japanese Patent Laid-Open No. 61-27741 discloses a method for detecting changes in heater resistance due to cracks.

[Problems to be Solved by the Invention] However, in the method described in the above publication, it is necessary to separately provide a grounding resistor for measuring the heater current, which requires installation space and also reduces the supply power. Furthermore, depending on the change in resistance value, it is not possible to accurately determine the local temperature rise or expansion of temperature difference on the glass surface, which actually causes glass deterioration.

The present invention has been made in view of this background, and it is an object of the present invention to provide a glass with a heater that accurately detects and warns of temperature changes on the glass surface due to cracks without providing a grounding resistor or the like.

[Means for Solving the Problems] The present invention effectively detects and issues an alarm on temperature changes on a glass surface due to cracks using a small number of temperature sensors, and has the following configuration.

That is, to explain the present invention in detail with reference to FIG. 1, current-carrying electrodes 2.3 are formed along two opposing sides of a glass substrate 1, and a heater made of a transparent conductive film is placed on the glass surface between these electrodes 2.3. The heated glass on which the film 4 is formed includes at least the glass surface of any of the above-mentioned current-carrying electrodes 2.3 near one end 21 to which the power supply line 51 is connected, and the glass surface near the other end 32 to which the above-mentioned power supply line is not connected. Temperature sensor 6A on the surface,
6B, and outputs an alarm when the detected temperature difference between the temperature sensors 6A and 6B exceeds a predetermined value, or when the temperature detected by the temperature sensor 6A installed near the one end 21 exceeds another predetermined value. An alarm means 7 is provided.

[Function] In the heater-equipped glass having the above configuration, the power supply line 51.5
2, when the heater film 4 is energized, the temperature distribution on the heater film 4 becomes highest in the part between the one end 21.31 of the two current-carrying electrodes 2.3, and gradually increases toward the part between the other end 22.32. Although it is lower, this temperature difference is not that large.

Therefore, the detected temperature difference between the temperature sensors 6A and 6B does not exceed the predetermined value. In addition, the above one end 2
The temperature of the heater film 4 portion between 1.31 and 1.31 does not rise excessively, and therefore the temperature detected by the temperature sensor 6A does not exceed the other predetermined value.

Now, if a crack occurs in the glass substrate 1 near the current-carrying electrode 2.3 and the current-carrying electrode 2.3 is disconnected in the middle, the subsequent electrode section up to the other end 22.32 and the other current-carrying electrode opposite thereto will be damaged. No current flows through the portion of the heater film 4 located between 3.2 and the temperature of this portion of the heater film 4 does not rise. On the other hand, the electrode portion of the current-carrying electrode 2.3 from its one end 21.31 to the disconnection portion, and the other current-carrying electrode 3 opposite thereto.
．． In the portion of the heater film 4 between the two, the current density increases and the temperature rises.

As a result, the temperature difference detected by both temperature sensors 6A and 6B exceeds the predetermined value, or the temperature detected by the temperature sensor 6A provided near one end exceeds the other predetermined value.

In this case, an alarm output is issued by the alarm means 7, and the heater energization is stopped, or measures such as replacement of the heater glass are prompted.

[First Embodiment] In FIG. 1, a glass substrate 1 used for a vehicle windshield glass is a trapezoidal laminated glass, and strip-shaped current-carrying electrodes 2. These current-carrying electrodes 2.3 are formed and face each other.
A similar trapezoidal transparent conductive film is formed on the glass surface between the heater films 4 and 3, and serves as a heater film 4.

A power supply line 5] 4.52 is connected to one end 21.31 of each of the current-carrying electrodes 2, 3, which leads to an on-board battery (not shown) or a power source that generates a voltage higher than the on-board battery voltage.
When energized, the heater film 4 generates heat and its temperature rises.

Thermistors 6A and 6B serving as temperature sensors are installed on the glass surface near one end 21 of the current-carrying electrode 2 and the glass surface near the other end 32 of the current-carrying electrode 3 that is far from the power supply part. Each is connected to an alarm circuit 7 outside the glass substrate 1, the details of which will be described later. Note that the resistance value of the thermistors 6A and 6B increases in proportion to the temperature of the glass surface of the installed portion.

Details of the alarm circuit 7 are shown in FIG. 2. In the figure, each thermistor 6A, 6B has a resistance 701.702, respectively.
are connected in series, the voltage Vk at the connection point is input to the "+" terminal of the comparator 71 and the "+" terminal of the differential amplifier 72, and the voltage ρ at the connection point is input to the "-" terminal of the differential amplifier 72.
” terminal. The output cuff 2a of the differential amplifier 72 is at the voltages Vk, V, l! This is input to the "+" terminal of the comparator 73.

A resistor-divided constant voltage vb is input to the "-" terminal of the comparator 71, and a resistor-divided constant voltage Va is input to the "-" terminal of the comparator 73. The outputs 1a and 73a of both the comparators 71 and 73 are input to an OR gate 74, and the output of the gate 74 is used as the transistor 7.
5.76 is activated. An alarm indicator light 77 is connected to the transistor 75. Further, a relay coil 78 is connected to the transistor 76, and its relay contact 78a is a normally closed contact, which is interposed in the power supply line 51, and becomes open when activated.

The operation of such heated glass will be explained below.

The temperature distribution of the above-mentioned electrode film 4 during energization is as follows:
It is highest in the part between one end 21 and 31 of 3, and gradually becomes lower towards the part between the other end 22 and 32,
Temperature difference Td between the above one end 21.31 and the other end 22.32
expands over time. However, if we look at the time course of the temperature T1 near one end 21 and the temperature T2 near the other end, we get something like the one shown in Figure 3, and the temperature difference Td tends to increase with time, but normally For example, when the outside temperature is -20°C and the amount of icing is 400cc, the temperature is relatively small at about 10°C even after the usual 4-minute energization.

Further, the temperature T1 does not reach the upper limit temperature Tu allowed for the durability of the glass substrate 1.

Therefore, in Figure 2, the signal ? Since the voltage 2a<Va and Vk<Vb, the transistor 75.7
6 are non-conductive, the alarm indicator light 77 is not lit, and the relay contact 78a is closed.

Now, if a crack occurs in the glass substrate 1 at the position shown by the point X in FIG. Temperature T of the glass surface near the other end 31 of the opposing current-carrying electrode 3
The increase in 2 is uneven (Figure 5). On the other hand, due to disconnection,
The current density increases in the heater film 4 near one end 21 of the current-carrying electrode 2, and the temperature T1 of the glass surface may rise rapidly at this portion and exceed the upper limit temperature Tu. Furthermore, in this case, the temperature difference Td also increases.

Therefore, in FIG. 2, the voltage of the signal 72a>Va, or Vk>Vb, and the voltage of the transistor 75.
76 becomes conductive, the alarm indicator light 77 lights up, and the relay contact 78a opens to stop the current supply to the heater membrane 4.

Further, if a crack occurs in the glass substrate 1 at the position indicated by the point X in FIG. 6 and the current-carrying electrode 3 is disconnected at this point, the electrode section from the disconnection point to the other end 32 will not be energized. The temperature T2 of the glass surface near the other end 32 also hardly rises, as shown in FIG. Then, as in the case of the above-mentioned wire breakage, the temperature T1 may rise rapidly and exceed the upper limit temperature Tu, and the temperature difference Td also increases.

Thus, in this case as well, the alarm indicator light 77 lights up and the electricity supply to the heater membrane 4 is stopped.

[Second Embodiment] FIG. 8 shows an example of a circuit that replaces the differential amplifier 72 and comparator 73 of the alarm circuit 7 in the above embodiment. In the figure, resistor 703, 704, 705, thermistor 6A
, and a thermistor 6B in which a resistor 706 is connected in series.
constitutes a bridge circuit, and the output of the bridge circuit is connected to the "+" terminal of the comparator 79 and the "-" terminal via a resistor.
” terminal.

In such a circuit, when a break occurs in the current-carrying electrode 2.3 due to a crack, the temperature of the thermistor 6A installation part increases and its resistance value increases, and when the difference with the resistance value of the thermistor 6B becomes larger than a certain value, The "+" terminal input of the comparator 79 becomes larger than the "-" terminal input, and "
1" level output cuff 9a.

Such a circuit configuration also has the same effects as the first embodiment.

As shown in each of the above embodiments, the thermistor must be provided at least near one end and the other end of the current-carrying electrode,
If detailed information on the disconnection position and temperature gradient is desired, a thermistor may be provided at another position.

Further, the thermistor need not be installed at one end and the other end of different current-carrying electrodes as in the above embodiment, but may be installed along the same current-carrying electrode.

Other temperature sensors besides thermistors can be used, such as platinum resistors.

[Effects of the Invention] As described above, according to the heater-equipped glass of the present invention, the durability of the glass can be improved by effectively detecting the local temperature rise and sudden increase in temperature gradient of the glass substrate due to cracks. This is something that can prevent the decline.

[Brief explanation of drawings]

1 to 7 show a first embodiment of the present invention.
The figure is a schematic front view of the glass with a heater, Figure 2 is a circuit diagram of the alarm circuit, Figure 3 is a diagram showing the change in temperature of the thermistor installation part over time, and Figure 4 is a schematic front view of the glass with a heater showing an example of a crack. Figure 5 is a diagram showing the change over time in the temperature of the thermistor installation part in that case, Figure 6 is a schematic front view of the heated glass showing another example of cracking, and Figure 7 is the temperature of the thermistor installation part in that case. FIG. 8 is a circuit diagram of a main part in a second embodiment of the present invention. 1... Glass substrate 2.3... Current-carrying electrode 21.31... One end 22.32... Other end 4... Heater film 51.52... Power supply lines 6A, 6B... Thermistor (Temperature sensor) 7...Alarm circuit (alarm means) Figure 1 Figure 2 O Figure 3 Time Figure 6 Figure 7 Figure 4 Figure 5 Figure 8

Claims (1)

[Claims] Forming current-carrying electrodes along two opposing sides of the glass substrate,
In a heated glass in which a heater film made of a transparent conductive film is formed on the glass surface between these electrodes, at least the glass surface of one of the above-mentioned current-carrying electrodes near one end to which the power supply line is connected is connected to the above-mentioned power supply line. A temperature sensor is provided on the glass surface near the other end of the glass, and the detected temperature difference between the two temperature sensors exceeds a predetermined value, or the temperature detected by the temperature sensor provided near the one end exceeds another predetermined value. 1. Glass with a heater, characterized in that it is provided with an alarm means that sometimes issues an alarm output.