Electrochromic mirror with automatic glare-proof function

Abstract: A rear view mirror assembly (1) with an automatic glare-proof function includes a battery (E1), a daytime/nighttime deciding circuit (3) for deciding whether the current time is daytime or nighttime, an integrating circuit (4), an electronic switch (FET1), a glare-proof/non-glare-proof deciding circuit (5) for deciding whether an electrochromic mirror element (2) is to be set to a glare-proof state or a non-glare-proof state, and a driving circuit (6) for applying a DC voltage to the electrochromic mirror element (2). The daytime/nighttime deciding circuit (3) is constantly applied with a DC voltage from the battery (E1). When the daytime/nighttime deciding circuit (3) decides that the current time is daytime, the electronic switch (FET1) is turned off, and when the daytime/nighttime deciding circuit (3) decides that the current time is nighttime, the electronic switch (FET1) is turned on. Therefore, the voltage is applied to the glare-proof/non-glare-proof deciding circuit (5) and the driving circuit (6) only when a decision has been made that the current time is nighttime. Thereby, the power consumption of the battery (E1) can be decreased.

Description: The present invention relates to a mirror assembly, for example a vehicle rear view mirror, with an adjustable reflectance by having an electrochromic mirror element (EC mirror) mounted on the vehicle, and relates, more particularly, to a technique for reducing power consumption of the EC mirror. When a driver is driving a vehicle at night or otherwise in the dark, it often occurs that light beams from the headlights of following vehicles are reflected by the rear view mirrors (outer and/or inner mirrors) and enter the driver's visual field so that the driver is dazzled by the glare of the beams. In order to prevent this problem, there exists an EC mirror having an electrochromic element (EC element) mounted on a rear view mirror and arranged such that a DC voltage is applied to this EC element to change the reflectance of the mirror, thereby preventing the driver from being dazzled by the glare of light irradiated from a vehicle following the driver's vehicle. As is widely known, when a DC voltage is applied to two input terminals in a forward direction, the surface of the EC mirror is colored to reduce the light reflectance so that the driver is prevented from being dazzled by the light reflected from the mirror. When a DC voltage is applied to the two input terminals in a reverse direction or when the two input terminals are short-circuited, it is possible to return the light reflectance of the EC mirror to the original state. Such an EC mirror has been disclosed, for example, in Japanese Utility Model Registration Publication No. 60540/94 (hereinafter referred to as a conventional example). Fig. 5 is an explanatory diagram showing a configuration of an EC mirror and its driving circuit of this conventional example. As shown in Fig. 5, a DC power source 105 is connected to two input terminals 102 and 103 of an EC mirror element 101 via a two-contact type and two-way switch 104. When the switch 104 is operated to apply a voltage output from the DC power source 105 so as to connect the input terminal 102 to a positive electrode and the input terminal 103 to a negative electrode, the EC mirror 101 is colored on its surface, which results in lowering of light reflectance. On the other hand, when the switch 104 is operated to apply a voltage output from the DC power source 105 so as to connect the input terminal 102 to a negative electrode and the input terminal 103 to a positive electrode, the EC mirror 101 is discolored on its surface, which allows the light transmittance to be returned to the original state. Based on these operations, it is possible to change between a glare-proof and a non-glare-proof mode. According to the driving circuit of the above-described conventional EC mirror, however, it is necessary to keep the switch 104 depressed for a predetermined period of time in order to color or discolor the surface of the EC mirror 101, which is troublesome. In other words, the EC mirror 101 has a characteristic that the surface of the EC mirror 101 is gradually colored when a voltage is applied continuously to the input terminals 102 and 103 in a forward direction for a predetermined period of time, and that the EC mirror 101 is gradually discolored when a voltage is applied continuously to the input terminals 102 and 103 in a reverse direction for a predetermined period of time. Therefore, the driver needs to keep depressing the switch. US-A-5,883,605 discloses a mirror assembly including features as in the pre-characterising part of claim 1. The present invention seeks to provide a mirror with an improved anti-glare function. According to an aspect of the present invention, there is provided a mirror assembly as specified in claim 1. The preferred embodiment can provide a back mirror having an automatic glare-proof function capable of automatically switching between the coloring and discoloring of an EC mirror and capable of reducing power consumption of a DC power source. More specifically, the preferred embodiment provides a rear view mirror having an automatic glare-proof function, in which a DC voltage output from a battery E1 is normally supplied to a daytime/nighttime deciding circuit. Based on this arrangement, a first surrounding light sensor makes a decision as to whether it is currently daytime or nighttime. When a decision has been made that the current time is daytime, an integrating circuit operates to turn off an electronic switch, thereby stopping a supply of DC voltage to a glare-proof/non-glare-proof deciding circuit and a driving circuit. On the other hand, when a decision has been made that it is nighttime, the integrating circuit operates to turn on the electronic switch, thereby starting a supply of DC voltage to the glare-proof/non-glare-proof deciding circuit and the driving circuit. The integrating circuit is set with a first time constant and a second time constant so that the time required for changing a decision from daytime to nighttime and the time required for changing a decision from nighttime to daytime can be set separately. When a DC voltage has been applied to the glare-proof/non-glare-proof deciding circuit in this embodiment, a decision is made based on a rear view light sensor and a second surrounding light sensor as to whether the EC mirror is to be set to a glare-proof state or a non-glare-proof state. In other words, when the illuminance of the light from the back is large, the glare-proof/non-glare-proof deciding circuit outputs a signal that makes the EC mirror to the glare-proof state, and when the illuminance of the light from the back is small, the glare-proof/non-glare-proof deciding circuit outputs a signal that makes the EC mirror to the non-glare-proof state. When the glare-proof/non-glare-proof deciding circuit has output a glare-proof state signal, the driving circuit applies a DC voltage to the EC mirror so that the EC mirror is set to a colored state, that is the glare-proof state. On the other hand, when the glare-proof/non-glare-proof deciding circuit has output the non-glare-proof state signal, the driving circuit short-circuits between two input terminals of the EC mirror so that the EC mirror in a colored state is switched to a discolored state, that is the non-glare-proof state. In this way, it is possible to change over automatically between the glare-proof state and the non-glare-proof state. In another embodiment, there is provided a rear view mirror having an automatic glare-proof function, in which when the daytime/nighttime deciding circuit has made a decision that the current time is nighttime, a DC voltage output from the battery is applied to the glare-proof/non-glare-proof deciding circuit and the driving circuit. Therefore, it is possible to reduce substantially the power consumption of the battery, which increases battery life. In addition, since the glare-proof state and the non-glare-proof state of the EC mirror can be automatically changed, a driver does not need to actuate any change over between the glare-proof state and the non-glare-proof state. As a result, a good operability as well as improvement of safety during the driving of the vehicle can be achieved. Advantageously, the daytime/nighttime deciding circuit comprises a first Schmitt trigger circuit, which makes it possible to prevent an occurrence of hunting without making a reaction to a slight change in the surrounding light. As a result, a secure decision can be made between the daytime and nighttime. Embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a circuit diagram showing a structure of an embodiment of rear view mirror having an automatic glare-proof function; Fig. 2 is an explanatory diagram showing hysteresis characteristics of a first Schmitt trigger circuit for the mirror of Figure 1; Fig. 3 is an explanatory diagram showing hysteresis characteristics of a second Schmitt trigger circuit for the mirror of figure 1; Fig. 4 is a timing diagram showing a state of on/off controlling of a voltage applied to an EC mirror; and Fig. 5 is a circuit diagram of a conventional EC mirror. Fig. 1 is an explanatory diagram showing one embodiment of a rear view mirror. It will be apparent, however, that the teachings herein could be applied to other types of mirror, not just rear view mirrors. As shown in Fig. 1, a rear view mirror 1 includes a battery E1 for outputting a DC voltage, an EC mirror (electrochromic mirror) element 2, a daytime/nighttime deciding circuit 3 for deciding whether the current time is daytime or nighttime, an electronic switch FET1 connected to the battery E1, and an integrating circuit 4 for turning off the electronic switch FET1 based on a first time constant when the daytime/nighttime deciding circuit 3 has decided that the current time is daytime and for turning on the electronic switch FET1 based on a second time constant when the daytime/nighttime deciding circuit 3 has decided that the current time is nighttime. The rear view mirror 1 also includes a glare-proof/non-glare-proof deciding circuit 5 for deciding whether the EC mirror 2 is to be set to a glare-proof state or a non-glare-proof state based on the brightness of the surroundings of the vehicle and the brightness at the rear of the vehicle, and a driving circuit 6 for applying a DC voltage to between two input terminals Ta and Tb of the EC mirror 2 when the glare-proof/non-glare-proof deciding circuit 5 has decided that the EC mirror 2 is to be set to the glare-proof state and for short-circuiting between the two input terminals Ta and Tb of the EC mirror 2 when the glare-proof/non-glare-proof deciding circuit 5 has decided that the EC mirror 2 is to be set to the non-glare-proof state. The daytime/nighttime deciding circuit 3 has a circuit having a resistor R1 and a first surrounding light sensor S1 connected in series. A DC voltage output from the battery E1 is applied to both ends of the series-connected circuit. The first surrounding light sensor S1 is composed of a CdS element (cadmium sulfide element), and has a large resistance when the illuminance of the surrounding light is small and a small resistance when the illuminance of the surrounding light is large. To a connection point P1 between the resistor R1 and the first surrounding light sensor S1, there is connected a first Schmitt trigger circuit (a first hysteresis circuit) IC1-1 for providing an inverted output signal. When the surroundings have become bright and the resistance of the first surrounding light sensor S1 has become small, the voltage at the contact point P1 becomes small. As a result, the input signal at the first Schmitt trigger circuit IC1-1 becomes an "L" (low) level and its output signal becomes an "H" (high) level (when a decision has been made that the current time is daytime). On the other hand, when the surroundings have become dark and the resistance of the first surrounding light sensor S1 has become large, the voltage of the contact point P1 becomes large. As a result, the output signal of the first Schmitt trigger circuit IC1-1 becomes the "L" level (when a decision has been made that the current time is nighttime). Since the first Schmitt trigger circuit IC1-1 has hysteresis characteristics, the brightness of the surrounding light (a first luminance level) when the output signal of the first Schmitt trigger circuit IC1-1 has become the "L" level following a rise in the voltage of the point P1 (that is, following the darkening of the surroundings) is different from the brightness of the surrounding light (a second luminance level) when the output signal of the first Schmitt trigger circuit IC1-1 has become the "H" level following a fall in the voltage of the point P1 (that is, following the brightening of the surroundings). This will be explained referring to the hysteresis characteristics shown in Fig. 2. When the surroundings have become bright and, for example, the luminance has become 60 lux or above (the second luminance level), the daytime/nighttime deciding circuit 3 decides that the current time is daytime (that is, the output of the IC1-1 is at the "H" level). When the surroundings have become dark, for example, the luminance has become 15 lux or below (the first luminance level ) after the luminance became 60 lux or above, the daytime/nighttime deciding circuit 3 decides that the current time is nighttime(that is, the output of the IC1-1 is at the "L" level). The integrating circuit 4 shown in Fig. 1 comprises a fifth Schmitt trigger circuit IC1-5, resistors R2 and R3, diodes D1 and D2, and a capacitor C1. The fifth Schmitt trigger circuit IC1-5 has characteristics similar to those of the first Schmitt trigger circuit IC1-1 described above, and has its input terminal (point P2) divided into four branch lines. A first branch line is connected to a positive electrode of the battery E1 via the diode D2. A second branch line is connected to an output terminal of the daytime/nighttime deciding circuit 3 (an output terminal of the first Schmitt trigger circuit IC1-1) via a circuit of the resistor R2 and the diode D1 connected in series. A third branch line is connected to an output terminal of the daytime/nighttime deciding circuit 3 via the resistor R3. A fourth branch line is connected to a negative electrode of the battery E1 via the capacitor C1. An output terminal of the fifth Schmitt trigger circuit IC1-5 is connected to a gate terminal of the electronic switch FET1. The electronic switch FET1 is turned on when the output signal of the Schmitt trigger circuit IC1-5 has become the "H" level, and is turned off when the output signal of the Schmitt trigger circuit IC1-5 has become the "L" level. The glare-proof/non-glare-proof deciding circuit 5 comprises, in this example, a rearward light sensor S3 structured by a CdS element, a second surrounding light sensor S2 structured by a CdS element, a second Schmitt trigger circuit (a second hysteresis circuit) IC1-2, a resistor R4 and a capacitor C2. The rearward light sensor S3 and the second surrounding light sensor S2 are mutually connected in series. One end of this series-connected circuit is connected to the positive electrode of the battery E1. A connection point P3 between the backward light sensor S3 and the second surrounding light sensor S2 is connected to an input terminal of the second Schmitt trigger circuit IC1-2. This connection point P3 is also connected to the input terminal Tb of the EC mirror 2 via the resistor R4 and is also connected to the input terminal Tb of the EC mirror 2 via the capacitor C2. The resistance value of the rearward light sensor S3 changes in response to the brightness at the rear of the vehicle. The resistance becomes small when the illuminance is large (that is, the rear is bright), and the resistance becomes large when the illuminance is small (that is, the rear is dark). The resistance of the second surrounding light sensor S2 changes in response to the brightness at the surrounding of the vehicle. The resistance value becomes small when the illuminance is large (that is, the surroundings are bright), and the resistance becomes large when the illuminance is small (that is, the surroundings are dark). Therefore, the voltage at the point P3 changes to become large when the rear has become bright and the surroundings have become dark while the electronic switch FET1 is on. On the other hand, the voltage of the point P3 changes to become small when the rear has become dark and the surroundings have become bright. Since the second Schmitt trigger circuit IC1-2 has hysteresis characteristics, the glare of the surrounding light (a first glare level) at the time when the output signal of the second Schmitt trigger circuit IC1-2 has become the "L" level following a rise in the voltage of the point P3 (that is, following the increase in the illuminance at the rear) is different from the glare of the surrounding light (a second glare level) when the output signal of the first Schmitt trigger circuit IC1-2 has become the "H" level following a fall in the voltage of the point P3 (that is, following the decrease in the illuminance of the rear light). This will be explained with reference to the hysteresis characteristics shown in Fig. 3. For example, when the rear has become bright and also the degree of glare the driver feels has become larger than "a large glare" (the first glare level), a signal showing the glare-proof state is output (that is, the output signal of the second Schmitt trigger circuit IC1-2 is set to the "L" level). Thereafter, when the rear has become dark and the degree of glare the driver feels has reduced and has become smaller than "a small glare" (the second glare level), a signal showing the non-glare-proof state is output (that is, the output signal of the second Schmitt trigger circuit IC1-2 is set to the "H" level). The driving circuit 6 shown in Fig. 1 comprises a third Schmitt trigger circuit (a third hysteresis circuit) IC1-3 and a fourth Schmitt trigger circuit IC1-4 mutually connected in series, four NOR circuits (logic circuits) IC2-1 to IC2-4, a diode D3, resistors R5 and R6, and a short-circuiting switch FET2. The third Schmitt trigger circuit IC1-3 is provided with a second threshold value Vmax and a first threshold value Vmin which is smaller than the Vmax. As a result, when a voltage applied to the third Schmitt trigger circuit IC1-3 has exceeded the second threshold value Vmax, an output signal of the IC1-3 becomes the "L" level. And when the voltage applied to the third Schmitt trigger circuit IC1-3 has become smaller than the first threshold value Vmin, the output signal of the IC1-3 becomes the "H" level. The four NOR circuits IC2-1 to IC2-4 are connected in parallel, respectively. One input terminal of each of the NOR circuits IC2-1 to IC2-4 is connected to the output terminal of the glare-proof/non-glare-proof deciding circuit 5 (the output terminal of the second Schmitt trigger circuit IC1-2), and the other input terminal of each of the NOR circuits IC2-1 to IC2-4 is connected to an output terminal of the fourth Schmitt trigger circuit IC1-4. A DC voltage is supplied to each of the NOR circuits IC2-1 to IC2-4 from the battery E1. An output signal of each of the NOR circuits IC2-1 to IC2-4 is connected to the input terminal Ta of the EC mirror 2 via the diode D3 and the resistor R6. A connection point P4 between the diode D3 and the resistor R6 is connected to the input terminal of the third Schmitt trigger circuit IC1-3 via the resistor R5. Furthermore, this connection point P4 is connected to the input terminal Tb of the EC mirror 2 via the short-circuiting switch FET2. A gate of the short-circuiting switch FET2 is connected to the output terminal of the glare-proof/non-glare-proof deciding circuit 5 (the output terminal of the second Schmitt trigger circuit IC1-2). Next, the operation of the embodiment having the above-mentioned structure will be explained. As shown in Fig. 1, since a DC voltage supplied from the battery E1 is always applied to the daytime/nighttime deciding circuit 3, a voltage signal is generated at the connection point P1 between the first surrounding light sensor S1 and the resistor R1. When the surrounding of the vehicle is bright (that is, during daytime), the resistance of the surrounding light sensor S1 becomes small, so that the voltage of the point P1 is small. Therefore, the input signal of the first Schmitt trigger circuit IC1-1 becomes the "L" level, and the output signal of the IC1-1 becomes the "H" level so that a voltage is applied to the capacitor C1 mounted on the integrating circuit 4 based on a time constant (the first time constant) determined by the capacitor C1 and the resistor R3. After the application of the voltage to the capacitor C1 has been completed, the voltage at the point P2 becomes the "H" level so that the output signal of the fifth Schmitt trigger circuit IC1-5 becomes the "L" level, thereby the electronic switch FET1 is turned off. As a result, the voltage output from the battery E1 is not applied to the glare-proof/non-glare-proof deciding circuit 5 and the driving circuit 6. In other words, when the surrounding of the vehicle is bright, a power source voltage is not supplied to the circuit that changes over the EC mirror 2 from the glare-proof state to the non-glare-proof state or from the non-glare-proof to glare-proof state (although, a voltage is applied to the NOR circuits IC2-1 to IC2-4). When the surroundings of the vehicle have become dark and thereby the resistance of the first surrounding light sensor S1 has become large, the voltage of the point P1 rises. As shown in Fig. 2, when the luminance of the surrounding light has become 15 lux or lower, the output signal of the first Schmitt trigger circuit IC1-1 is changed over from the "H" level to the "L" level (when a decision is made that the current time is nighttime). In this case, because the first Schmitt trigger circuit IC1-1 has hysteresis characteristics as described above, there will not occur a problem such as hunting of the output signal in response to a slight change in the surrounding light. When the output signal of the first Schmitt trigger circuit IC1-1 has become the "H" level, the capacitor C1 is discharged via the parallel-connected circuit of the resistor R2 and the resistor R3. The time constant (the second time constant) in this case is determined by a parallel combined resistance of the resistor R2 and the resistor R3 and an electrostatic capacity of the capacitor C1. The voltage can be discharged in a shorter time than the time required for charging. When the capacitor C1 has been discharged, the voltage at the point P2 becomes the "L" level and the output signal of the fifth Schmitt trigger circuit IC1-5 becomes the "H" level, so that the electronic switch FET1 is turned on. As a result, a voltage output from the battery E1 is applied to the glare-proof/non-glare-proof deciding circuit 5 and the driving circuit 6. In this case, since the fifth Schmitt trigger circuit IC1-5 has hysteresis characteristics, there will not occur a problem such as hunting in response to a slight voltage variation at the point P2. When the electronic switch FET1 is turned off, a DC voltage output from the battery E1 is applied to the circuit connected in series between the rearward light sensor S3 and the second surrounding light sensor S2 of the glare-proof/non-glare-proof deciding circuit 5. Then, the voltage at the connection point P3 between the rearward light sensor S3 and the second surrounding light sensor S2 changes according to the illuminance of the surrounding light and the illuminance of the rearward light. For example, when the headlight beams of a vehicle following the vehicle having the mirror described herein are focused on the vehicle while the surroundings of the vehicle are dark, the resistance of the rearward light sensor S3 decreases while the resistance of the surrounding light sensor S2 increases. As a result, the voltage at the point P3 rises to reach the "H" level and the output signal of the second Schmitt trigger circuit IC1-2 becomes the "L" level. As no voltage has been applied between the input terminals Ta and Tb of the EC mirror 2, the voltage at the point P4 is at the "L" level and the output signal of the fourth Schmitt trigger circuit IC1-4 becomes the "L" level. Therefore, all the input signals of the four NOR circuits IC2-1 to IC2-4 become the "L" level, and their output signals become the "H" level. As a result, the voltage of the point P4 is switched from the "L" level to the "H" level so that a DC voltage will be applied between the two input terminals Ta and Tb of the EC mirror 2 in the forward direction in which the Ta becomes the positive electrode, and the Tb becomes the negative electrode. Thus, the surface of the EC mirror 2 becomes gradually colored to have a reduced reflectance, so that the EC mirror 2 is set to the glare-proof state. When the voltage of the point P4 has become the "H" level, the voltage between the input terminals Ta and Tb of the EC mirror 2 gradually increases. When this voltage has exceeded the second threshold value Vmax of the third Schmitt trigger circuit IC1-3, the output signals of the third Schmitt trigger circuit IC1-3 and the fourth Schmitt trigger circuit IC1-4 are inverted respectively, while the output signal of the fourth Schmitt trigger circuit IC1-4 becomes the "H" level. Thus, all the output signals of the four NOR circuits IC2-1 to IC2-4 become the "L" level, and the voltage of the point P4 becomes the "L" level. As a result, the supply of voltage to the EC mirror 2 is stopped. Thereafter, when the voltage between the two terminals Ta and Tb of the EC mirror 2 gradually decreases to become smaller than the first threshold value Vmin of the third Schmitt trigger circuit IC1-3, the output of the fourth Schmitt trigger circuit IC1-4 becomes the "L" level so that the supply of voltage to the EC mirror 2 is started again. As a result, the application of voltage supply and the disconnection of the voltage supply to the input terminals Ta and Tb of the EC mirror 2 are repeated alternately as shown in Fig. 4, thereby the colored state of the EC mirror 2 will be maintained. In other words, as shown in Fig. 4, a voltage is applied to the input terminals Ta and Tb of the EC mirror 2 between times t1 and t2 to set the EC mirror 2 to the colored state such that when the voltage for coloring the EC mirror 2 has become Vmax at the time t1, the supply of voltage to the EC mirror 2 is stopped, and when the voltage for colouring has become Vmin at the time t3, the supply of voltage is started again. By repeating this operation, the colored state of the EC mirror 2 can be maintained, and as a result, power consumption of the battery E1 can be remarkably reduced. Furthermore, when the illuminance at the rear of the vehicle has dropped so that the resistance of the backward light sensor S3 shown in Fig. 1 has become large, the voltage at the point P3 is switched to the "L" level. As a result, the output signal of the second Schmitt trigger circuit IC1-2 becomes the "H" level, so that all the signals supplied to one input terminal of each of the four NOR circuits IC2-1 to IC2-4 become the "H" level. Therefore, regardless of the output signal of the fourth Schmitt trigger circuit IC1-4, all the output signals of the four NOR circuits IC2-1 to IC2-4 become the "L" level so that no voltage will be applied to the input terminals Ta and Tb of the EC mirror 2. At the same time, as the "H" level signal is supplied to the gate terminal of the short-circuiting switch FET2, the short-circuiting switch FET2 is turned on so that it is short-circuited between the input terminals Ta and Tb of the EC mirror 2 via the resistor R6. Thereby, the EC mirror 2 in the colored state is gradually discolored to return to the original state. In other words, when the headlight beams of a following vehicle are not illuminated, the reflectance of the EC mirror 2 returns to the original state (the non-glare-proof state). The colouring and the discolouring of the EC mirror 2 are automatically changed over in this manner. As explained above, in this embodiment, when the first surrounding light sensor S1 has decided that the current time is daytime, a DC voltage output from the battery E1 is not applied to the glare-proof/non-glare-proof deciding circuit 5 and the driving circuit 6. On the other hand, when the first surrounding light sensor S1 has decided that the current time is nighttime, the DC voltage is applied to the glare-proof/non-glare-proof deciding circuit 5 and the driving circuit 6. Therefore, based on this arrangement, it is possible to reduce power consumption of the battery E1 remarkably, which lengthens the lifetime of the batteries. Furthermore, since a small battery can be used for a long time, it is possible to lighten the circuit. Additionally, the switching from the glare-proof state to the non-glare-proof state or from the non-glare-proof to glare-proof state of the EC mirror 2 can be done automatically without requiring the driver to carry out any troublesome operation. Thus, safety of the system can also be improved. Moreover, since the daytime/nighttime deciding circuit 3 comprises a Schmitt trigger circuit IC1-1 having hysteresis characteristics, it is possible to avoid the problem that the output signal of the daytime/nighttime deciding circuit 3 brings about hunting in response to a slight change of the surrounding light around the vehicle. Furthermore, the time constant (the second time constant) used at the time of discharging the capacitor C1 mounted on the integrating circuit 4 is set faster than the time constant (the first time constant) for charging the capacitor C1. In other words, the time required for changing a determination from daytime to nighttime is set shorter than the time required for changing the determination from nighttime to daytime. Based on this setting, for example, when the vehicle has entered into a tunnel in daytime, a decision that the current time is nighttime can be made relatively fast, which enables the EC mirror 2 to be set as the glare-proof state. When the vehicle has exited the tunnel, the electronic switch FET1 can be turned off after the EC mirror 2 has been sufficiently discoloured. Since the first time constant is set long, such a problem that daytime is erroneously determined as nighttime can be prevented, for example, when the vehicle has passed under trees or under a railroad overpass. Furthermore, as shown in Fig. 4, when the EC mirror 2 is set to a coloured state by applying a DC voltage to the input terminals Ta and Tb, the coloured state of the EC mirror 2 will be maintained while the application of the voltage and the stopping of the application of the voltage to the input terminals Ta and Tb are carried out alternately. Thus, the power consumption of the battery E1 can be further reduced. Particularly, if a solid type EC mirror 2 having a memory function at the time of colouring the EC mirror 2 is used, leakage current will become small when the state between the input terminals Ta and Tb are released at the time of colouring so that it will require a longer time to decrease the voltage for colouring. Therefore, the time required for applying a voltage (between the times t3 and t4 shown in Fig. 4) can be made shorter than the time (between the times t2 ant t3) for not applying the voltage. Additionally, since the battery E1 is used as the DC power source, the installation work can be facilitated without requiring the connection of a wire harness between the vehicle main body and the mirror housing. Although a hysteresis circuit has been explained by using a Schmitt trigger circuit as an example in the above embodiment, this is not essential. Instead of the Schmitt trigger circuit, any circuits having hysteresis characteristics with an equivalent function can be used.

Claims: A mirror assembly with an automatic glare-proof function comprising an EC mirror element (2) and able to detect light surrounding and light facing the mirror assembly and operable to change the EC mirror element between a glare-proof state and a non-glare-proof state automatically in response to the results of the detection; said mirror assembly comprising daytime/nighttime deciding means (3) including a first surrounding light sensor (S1) operable to detect surrounding light around the mirror and operable to detect whether a current time is daytime or nighttime based on the result of the detection made by the first surrounding light sensor (S1); switching means (FET1) turned on when the daytime/nighttime deciding means (3) has decided that the current time is nighttime; glare-proof/non-glare-proof deciding means (5) including a second surrounding light sensor (S2) for detecting light surrounding the mirror and a backward light sensor (S3) for detecting light facing the mirror and activated when the switching means (FET1)has been turned on, glare-proof/non-glare-proof deciding means (5) being operable to decide the state in which the EC mirror element (2) is to be set on the basis of the results of the detection by the second surrounding light sensor (S2) and the backward light sensor (S3); and driving means (6) activated when the switching means (FET1) is turned on and operable to drive a coloring and an uncoloring of the EC mirror element (2) in response to the result of the decision made by the glare-proof/non-glare-proof deciding means (5), characterized in that that the glare-proof/non-glare proof deciding means (5) decides that the driving means should be activated to drive a coloring of the EC mirror element (2) when the glare has reached a first glare level or above and the glare-proof/non-glare proof deciding means (3) decides that the driving means should be activated to drive an uncolouring of the EC mirror element (2) when the glare is at a second glare level or below; wherein the first glare level is higher than the second glare level. A mirror assembly according to claim 1, wherein the daytime/nighttime deciding means (3) decides that the current time is nighttime when the luminance has reached a first luminance level or above and the daytime/nighttime deciding means (3) decides that the current time is daytime when the luminance has reached a second luminance level or below; wherein the first luminance level is lower than the second luminance level. A mirror assembly according to claim 1 or 2, wherein in the daytime/nighttime deciding means (3) the time required for changing from a determination from daytime to nighttime is set shorter than the time required for changing from a determination from nighttime to daytime. A mirror assembly according to claim 1, 2 or 3, wherein the driving means (6) is operable to apply and disconnect a voltage supply alternately to maintain the colored state of the EC mirror element (2). A mirror assembly according to any preceding claim, wherein the first surrounding light sensor (S1) includes a resistive element whose resistance varies according to the brightness of the surrounding light, and the daytime/nighttime deciding means (3) includes a series-connected circuit of the the first surrounding light sensor (S1) and a resistor in which a voltage output from a DC power source (E1) is applied to both ends of the series-connected circuit so that the daytime/nighttime deciding means (3) can detect a voltage at a connection point between the surrounding light sensor (S1) and the resistor so as to decide whether the current time is daytime or nighttime. A mirror assembly according to claim 2, wherein a first hysteresis circuit (IC1-1) is provided at the connection point between the first surrounding light sensor (S1) and the resistor so that the daytime/nighttime deciding means (30) decides whether the current time is daytime or nighttime on an output signal from the first hysteresis circuit (IC1-1). A mirror assembly according to any preceding claim, wherein there is provided an integrating circuit (4) operable to turn on the switching means (FET1) on the basis of a first time constant when an output signal of the daytime/nighttime deciding means (3) has been switched from a signal representative of nighttime to a signal representative of daytime and to turn off the switching means (FET1) on the basis of a second time constant when the output signal of the daytime/nighttime deciding means (3) has been switched from the signal representative of daytime to the signal representative of nighttime. A mirror assembly according to any preceding claim, wherein the backward light sensor (S3) and the second surrounding light sensor (S2) each include a resistive element whose resistance varies in response to the brightness of the surroundings, the glare-proof/non-glare-proof deciding means (5) includes a circuit connected in series between the backward light sensor (S3) and the second surrounding light sensor (S2), and a voltage output from a DC power source (E1) is applied to both ends of the series-connected circuit so as to decide whether the EC mirror element (2) is set to the glare-proof state or not based on the voltage at the connection point between the backward light sensor (S3) and the second surrounding light sensor (S2). A mirror assembly according to any preceding claim, wherein a second hysteresis circuit (IC1-2) is provided at the connection point between the backward light sensor (S3) and the second surrounding light sensor (S2) so that the glare-proof/non-glare-proof deciding means (5) decides whether the EC mirror element (2) is set to the glare-proof state or not on an output signal from the second hysteresis circuit (IC1-2). A mirror assembly according to any preceding claim, wherein the driving means (6) comprises a logic circuit (IC2) operable to apply a DC voltage to an input terminal of the EC mirror element (2) when the output signal from the glare-proof/non-glare-proof deciding means (5) is representative of a glare-proof state; and a third hysteresis circuit (CL1-3) provided with a first threshold value and a second threshold value larger than the first threshold value, in which a signal showing a stopping of a voltage supply to the EC mirror element (2) is output to the logic circuit (IC2) when a voltage for coloring the EC mirror element (2) has become equal to or larger than the second threshold value, and a signal showing a starting of the voltage supply to the EC mirror element (2) is output to the logic circuit (IC2) when a voltage for coloring the EC mirror element (2) has become equal to or smaller than the first threshold value. A mirror assembly according to any preceding claim, wherein the driving means (6) comprises a short-circuiting switch (FET2) for short-circuiting between the input terminals of the EC mirror element (2) when the output signal from the glare-proof/non-glare-proof deciding means (5) is representative of the non-glare-proof state. A mirror assembly according to any preceding claim, wherein the first and second surrounding light sensors (S1, S2) and the backward light sensor (S3) each include a cadmium sulfide element. A mirror assembly according to any preceding claim, wherein the EC mirror element (2) is of a solid type having a memory able to retain the reflectance at the time of coloring. A mirror assembly according to any preceding claim, wherein the assembly is a rear view mirror assembly for a vehicle.

Inventors: NAGAO MITSUYOSHI, SATO HIDENORI, NAGAO, MITSUYOSHI, SATO, HIDENORI
Applicants: MURAKAMI CORP, MURAKAMI CORPORATION
Application year: 2000
Main classification: B60R1
IPC codes: B60R1, G02F1