GB2142297A - A rear view mirror for a motor vehicle - Google Patents

Abstract

A rear view mirror for a motor vehicle, which rear view mirror comprises pivoting means (10) for causing the mirror (8) to pivot between normal and anti-glare positions in dependence upon the presence or absence of light of a predetermined intensity from a following vehicle, the pivoting means including ambient light compensation means (200). e.g. a pair of photosensors arranged in a bridge circuit, for compensating for the affect of ambient light on the pivoting means. <IMAGE>

Description

SPECIFICATION A rear view mirror for a motor vehicle This invention relates to a rear view mirror for a motor vehicle. More specifically, this invention relates to a rear view mirror for a motor vehicle that will pivot between normal and anti-glare positions in dependence upon the presence or absence of light of a predetermined intensity from a following vehicle.

Rear view mirrors for motor vehicles are known in which the mirror comprises pivoting means for causing the mirror to pivot between normal and anti-glare positions in dependence upon the presence or absence of light of a predetermined intensity from a following vehicle. Such mirrors work quite well and they may be provided with sensitivity adjuster means for adjusting the sensitivity of the mirror to the predetermined light intensity.

Normally, once the sensitivity is set, it will not again be adjusted.

Sometimes, a problem arises when a vehicle passes from relatively dark ambient light conditions such as are experienced when driving through open country at night, into relatively bright ambient light conditions such as are experienced when driving through town centres at night. If the sensitivity means has been set for relatively dark ambient light conditions, the relatively bright ambient light conditions will affect the sensitivity of the mirror and the mirror may switch prematurely from its normal to its anti-glare position. The relatively bright ambient light conditions will not in themselves be sufficient to make the mirror switch from its normal to its anti-glare position, but they may be sufficient to cause the premature switching when a following vehicle shines its lights on the vehicle having the pivoting mirror.This premature switching can provide a source of annoyance to the driver which can adversely affect his driving ability.

It is an aim of the present invention to provide a rear view mirror for a motor vehicle in which the problem of premature switching is reduced or obviated.

Accordingly, this invention provides a rear view mirror for a motor vehicle, which rear view mirror comprises pivoting means for causing the mirror to pivot between normal and anti-glare positions in dependence upon the presence or absence of light of a predetermined intensity from a following vehicle, the pivoting means including ambient light compensation means for compensating for the affect of ambient light on the pivoting means.

Preferably, the ambient light compensation means comprises a pair of photosensors arranged in a bridge circuit.

The rear view mirror may comprise a housing having a back plate portion and a front frame portion connected to the back plate portion to define a chamber for receiving the pivoting means.

The mirror may be pivotally mounted within the housing chamber, the lower edge of the mirror being arranged within the housing recess.

In addition to the ambient light compensating means, the pivoting means of the rear view mirror may include biasing means for biasing the mirror towards its normal position, a solenoid coil connected to the photosensors, and magnet means mounted on a rear portion of the mirror such that when light strikes the photosensors above the predetermined intensity, the solenoid coil generates a magnetic field which attracts the magnet means and causes the mirror to pivot to its antiglare position. It will be appreciated that when the light intensity falls below the predetermined level, the solenoid coil will cease to generate the required magnetic field and the magnet means will be released, where upon the biasing means will return the mirror to its normal position.

The rear view mirror will normally include sensitivity means for initially setting the predetermined light intensity at which the mirror is responsive. The sensitivity means is preferably a potentiometer, the potentiometer being provided with an adjustable thumb wheel.

Preferabiy, the rear view mirror is one which is mounted inside the motor vehicle. If desired~hswever, the rear view mirror may be mounted on the outside of the motor vehicle, for example on the vehicle wings or front doors.

Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 is a front elevation of an embodiment of a rear view mirror according to the invention, with the mirror glass partly broken away to show internal details of the mirror; Figure 2 is a cross-sectional view of the mirror taken along the line 11-11 of Figure 1, the mirror glass being shown in the normal viewing position; Figure 3 is an exploded sectional view of the mirror along the line 11-11 of Figure 1, the mirror glass being shown in the anti-glare position; Figure 4 is an exploded view on an enlarged scale of a ball and socket joint at the rear of the mirror housing coupling a mounting arm to the mirror; Figure 5 is a circuit diagram of part of the electrical assembly of the mirror;; Figure 6 is a circuit diagram of an alternative form of part of the electrical assembly of the mirror; Figure 7 is a circuit diagram of part of the electrical assembly of the alternative mirror of Figures 8 and 9; Figure 8 is a front elevational view of an alternative rear view mirror according to the invention; Figure 9 is a cross-sectional view of the mirror of Figure 8 taken along the line 11-11 of Figure 8; and Figure 10 is a circuit diagram showing an ambient light compensation circuit for the rear view mirrors.

Referring to Figures 1 to 4, there is shown a rear view mirror comprising a housing 2 formed as a synthetic plastics moulding in two parts, namely a back plate 4 and a front frame 6. Located between the two parts of the housing is a mirror glass 8 movable between a normal viewing position (Figure 2) and an anti-glare position (Figure 3) in which glare from light reflected from the mirror is reduced. The mirror is pivotable about a pivot 10. An electrical assembly includes a solenoid coil 1 6 which is energized in response to light incident upon the mirror above a predetermined intensity, the coil co-acting with a magnetic member 1 8 carried by the mirror glass to move the mirror glass from its normal position to an anti-glare position when the solenoid is energized.The mirror glass is held in its normal position in normal operation by means of a return spring 20. The mirror is mounted to the motor vehicle by means of a mounting arm 22 attached to the rear of the housing 2.

Referring now in more detail tothe construction of the housing, the back plate 4 is in the form of a tray with rear walls 30 (Figure 4) tapering to provide a deepened portion at the centre of the tray. Reinforcing ribs 32 are provided for strengthening the tray and the centre of the tray carries three fixing studs 34 to retain an electrical assembly 1 2. The rear of the back plate 4 provides a socket 36 of a ball and socket joint which serves to receive a ball member 38 of a mounting arm 22.

Mounting arm 22 is thus held mounted to the back plate 4 by means of a universal ball and socket joint. Socket 36 is designed to permit various configurations of mounting arms having different size end portions to be mounted to the back plate 4. Referring to the construction of socket 36 as shown in Figure 4, a boss portion 40 at the rear of the back plate has a vertical bore 42 of circular section which communicates with a slot 44 in the surface of the boss to permit the mounting arm 22 to extend from the bore 42. The top portion of the bore 42 is tapered as at 46 to permit ball joints of different sizes to make a good fit with the bore. This may occur where a motor vehicle has already been installed with an appropriate mounting arm.A locking member 48 is provided having a cylindrical portion 50 making a reasonably close fit within bore 42 and having a recessed top portion 52 providing a seat for ball 38. Locking member 48 is locked in position be means of two self tapping screws 54 extending through apertures 56 in wing portions 58 of locking member 48. Wing portions 58 are arranged to fit within recesses 60 of boss 40 and screws 54 extending into the interior of the back plate 4 to extend through registering apertures 62 in a reinforcing rib 32. Apertured spring steel clips 64 are mounted over apertures 62 in order to receive screws 54 and to engage the threads thereof so that screws 54 can be tightened to secure the locking member 48. The top of boss 40 has a ribbed surface 66.Mounting arm 22 shown has a flat surface 70 which may be adhesively mounted by means of an adhesive pad to the window of a motor vehicle. Reinforcing ribs 72 are provided on the other side of surface 70 in order to strengthen the surface and to prevent warping.

The front surface of the back plate 4 has at its base an aperture 80 through which part of the electrical assembly, a sensitivity adjustment thumb-wheel 82, projects. The front surface of the back plate 4 has apertures 84 spaced around the surface which serve in the securing of the front frame 6 to back plate 4.

Front frame 6 is generally rectangular in configuration and possesses projecting nodules 86 around its periphery which interengage with recesses 84 in back plate 4 as a snap fit in order to secure together back plate 4 and front frame 6. Front frame 6 has a recessed portion 88 in order to receive mirror glass 8. A further recessed portion 90 extends along the lower edge of the front of back plate 4 and co-operates with recess 88 in order to provide a longitudinal U-shaped recess. This U-shaped recess serves to support the lower edge of mirror glass 8 and to permit the mirror glass to pivot about pivot 10.As an alternative arrangement, recess 88 and recess 90 may be shaped to provide a recess circular in section and a cylindrical element may be provided to fit within the recess and to support the mirror glass 8, the lower edge of the mirror glass fitting within an axial slot in the cylindrical element.

Mirror glass 8 is of conventional construction. Mirror glass 8 is only partly silvered in the region 100 opposite photosensor 14 by providing a series of transparent lines in order to permit incident light to be transmitted through the mirror to photosensor 14. This arrangement provides a collimation effect for light passing through the mirror on to photosensor 14 and this renders the mirror more sensitive to light from headlamps of vehicles behind the motor vehicle containing the rear view mirror as compared with other lights, for example courtesy lights within the motor car or street lighting.

The electrical assembly 12 is formed as a single unit and includes a board 104 upon which the other elements of the assembly are mounted. The board has apertures registering with studs 34 in order to secure the assembly to back plate 4. Locking clips 106 are pro vided to fit on studs 34. The assembly is powered from a suitable circuit (e.g. sidelight circuit) energized by the vehicle battery and leads will be fed through the back plate 4 in a suitable manner. Photosensor 14, which may comprise a photodiode, is connected (see Figure 5) to a potentiometer in the form of a thumb-wheel 82 which regulates the sensitivity of the electrical assembly, i.e. the thumbwheel 82 predetermines the intensity of light incident upon the photosensor 14 at which the electrical assembly will be actuated to move the mirror to the anti-glare position.

The movable contact 106 of thumb-wheel 82 is connected by a series resistance 108 and a reverse biased diode 110, connected between resistor 108 and ground to the base of a transistor 11 2. The collector circuit of transistor 11 2 includes solenoid coil 1 6. A protect tion diode 114 is connected across solenoid coil 16. Solenoid coil 16 has a centre tapping which is connected to contacts 116.

Contacts 116 are closed when glass 8 is moved to the anti-glare position and are shown schematically in Figures 2 and 3.

As can be seen in Figures 2 and 3, the physical disposition of the electrical assembly is such that the core of the solenoid 1 6 is disposed remote from magnetic member 18 in the normal rest position of the mirror.

Magnetic member 18 is secured to the rear of mirror glass 8 by means of an adhesive pad 1 20 and the mirror glass is retained in the rest position by a return spring 20 coupled between an aperture in a depending tine 122 of magnetic member 1 8 and a tine 1 24 of an upstanding member 126. The edge 128 of member 1 26 remote from board 104 has a recess 1 30 to receive tine 1 22 which engages the base of the recess in order to provide said pivot 10 for the mirror.

Pads 140 adhesively secured to the mirror glass 8 are arranged to engage reinforcing ribs at 1 42 in order to provide a buffer when mirror glass 8 moves to the anti-glare position.

In operation of the rear view mirror so far described, light from headlamps of a vehicle approaching the motor vehicle in which the rear view mirror is mounted may cause light to be incident upon the rear view mirror and this light will be transmitted to the photosensor 14. If the intensity of the light is above a level determined by the setting of potentiometer 82, sufficient current will be generated in resistor 108 to switch transistor 110 from its normal non-conductive state to a fully conductive state. This causes energizing current to flow in the solenoid 16, which creates an electromagnetic field to attract magnetic member 1 8 and thus move mirror glass 8 about pivot 10 to the anti-glare position (Figure 3) in which the amount of light reflected from the mirror glass to the driver of the vehicle is reduced.Now the amount of current required to flow in the solenoid coil to move the mirror to the anti-glare position is considerably more than that required to hold the mirror in the anti-glare position. Accordingly when mirror glass 8 moves to the anti-glare position, contacts 11 6 are closed which has the effect of shorting out part of coil 1 6 and thus causing a reduced current flow in the solenoid. This current flow is sufficient to hold the mirror glass in the anti-glare position for as long as light above the predetermined intensity shines on the mirror glass. Reduction of the current flow through the solenoid coil permits a longer life expectancy for the components of the circuit assembly.

In the alternative form of electrical assembly shown in Figure 6, parts similar to those of Figure 5 are indicated by similar reference numerals. Transistor 11 2 serves to amplify the current generated in resistor 108 and a main switching transistor 1 50 is coupled to the collector circuit of transistor 1 10 via resistors 152, 1 54 and diode 1 56. Coil 1 6 is connected in the collector circuit of transistor 1 50 together with a series resistor 1 58. Contacts 11 6 which are closed in the normal position of mirror glass 8 are connected across resistor 1 58. This alternative form has a higher sensitivity to incident light by virtue of the amplification provided by transistor 110. When the coil 16 is energized to move mirror glass to the anti-glare position, contacts 11 6 are opened so that resistor 1 58 is switched into coil 1 6 in order to reduce current flow through coil 1 6 and provide a holding current.

Another embodiment of a rear view mirror according to the invention is shown in Figures 7 to 9. This embodiment is generally similar to that previously described and like parts are marked with like reference numerals.

As is shown in Figures 8 and 9, the mirror comprises a housing 2 consisting of a back plate part 4 and a front frame part 6 each moulded in a plastics material. The mirror glass 8 is located between the housing parts 4, 6 so as to be pivotally mounted at its bottom edge. Two return springs 20A, 20B urge the mirror glass 8 to pivot to a position abutting the frame 6 wherein the mirror glass is in its normal viewing position. The return springs 20 sit in cup shaped members 1 60 integrally moulded in the back plate 4.

An electrical assembly 12 is mounted in the housing 2 on studs 34 at the back of the back plate 4, as by gluing. The electrical assembly 1 2 is formed as a single unit wherein all of the illustrated electrical components of the mirror are mounted on a single circuit board 161. As with the previously described embodiment, the electrical assembly 1 2 includes a phtosensor 1 4 which receives light incident on the mirror glass 8 through an aperture 1 62 formed in the silvered layer 1 63 of the mirror glass, the assembly 1 2 further includ ing a potentiometer 82 with an adjustable thumbwheel projecting through a slotted aperture 80 in the back plate 4, the potentiometer being for adjusting the sensitivity of the circuit to incident light, as previously described.The assembly further includes a solenoid coil 1 6 which co-operates with a metal plate 164 carried by the mirror to pivot the mirror to its anti-glare position.

The coil 1 6 of the Figures 8 and 9 embodiment differs from that of the Figures 1 to 4 embodiment in that its axis is arranged generally parallel to the plate of the circuit board 1 61, the coil having generally L-shaped pole pieces 165, 1 66 which present flat surfaces which abut the metal plate 164 when the mirror is in its anti-glare position. This coil arrangement has the advantage of allowing a coil of a substantial number of turns to be included in the housing 2 without increasing the distance between the mirror glass 8 and the rear of the back plate 4.

The back plate 4 is formed with an integral socket 1 81 which receives a ball 182 of a mounting arm 167.

The circuit included on the printed circuit board 161 is shown in detail in Figure 7. The circuit is adapted to be connected to the vehicle's sidelight circuit through input terminals 168, 169. A protection diode 170 is provided to protect the circuit agalonst an incorrect polarity connection being made between the sidelight circuit and the mirror. A resistor 171 and a zener diode 172 act as a current limiting arrangement to ensure that the voltage established between the input terminals 168, 1 69 does not exceed a predetermined maximum value e.g. 18 volts, so as to protect the circuit.The photosensor 14 is connected between the input terminals 168, 1 69 in a potentiometer chain including resistors 1 73 to 175, whereby the potential at point 1 76 in the chain increases with increased illumination. This potential is compared with a selectively variable reference potential established by the potentiometer 82, by means of an operational amplifier 1 77 connected as a comparator. The output of the operational amplifier 1 77 is connected to a zener diode 1 78 and hence to the base of a control transistor 1 79 which controls the current flowing in the solenoid coil 16.A resistor 1 80 provides a current path for both the base leakage current of the transistor 1 79 and the leakage current of the diode 1 78.

In use, when increased illumination causes the potential at point 1 76 to exceed the reference voltage set by the potentiometer 82, the output of the amplifier 1 77 goes high.

When the output exceeds the threshold set by the zener diode 178, the transistor 179 is switched on, energizing the coil 1 6 which causes the mirror to move to its anti-glare position.

It will be seen that the described embodiments of the mirror can be assembled inexpensively and easily by virtue of the unitary nature of the electrical assembly 1 2 and the manner in which the mirror glass 8 is pivotally mounted at its edge by the housing parts 4 and 6. Thus, during assembly, the circuit assembly 1 2 is first attached to the rear of the back plate 4, the spring(s) 20 are appropriately installed, the mirror glass 8 is dropped into place, and front frame 6 is located in position. This simple construction method provides an extremely sensitive rear view mirror at reduced costs.

The circuits so far described with reference to Figures 5, 6 and 7 may allow the rear view mirror to prematurely pivot from its normal position to its anti-glare position. More specifically, when the vehicle passes from relatively dark ambient light conditions such as are experienced when driving through open country at night, into relatively bright ambient light conditions such as are experienced when driving through town centres at night, the relatively bright ambient light conditions may affect the sensitivity of the mirror and cause the premature switching.

In accordance with the present invention, the circuits of Figures 5, 6 and 9 are modified to include ambient light compensation means.

A typical ambient light compensating circuit will now be described by way of example only and with reference to Figure 10. Figure 10 specifically shows a modified part for the illustrated left hand part of the circuit shown in Figure 7. In Figure 10, similar parts as in Figure 7 have been given the same reference numerals.

In Figure 10, the modified circuit comprises in addition to the light detector 14, a light detector 200 which is connected in series with the light detector 14 and which is also connected to power supply lines 202 and 204 via a pair of similar current limiting resistors 206 and 208. The light detector 1 4 and the light detector 200 are connected in parallel with the potentiometer 82 and the amplifier 1 77 is fed with a signal developed between the wiper 210 of the potentiometer 82 and a line 212 which communicates with the junction between the light detectors 14 and 200.The light detector 1 4 is positioned in the driving mirror and arranged so as to receive at night light from head lights directed towards the rear of a car in which the mirror is fitted and the light detector 200 is positioned and arranged so as to receive ambient light. In order to arrange that the light detector 200 receives ambient light only, it is positioned so as to point generally downwardly away from the glare of street lighting or the glare of the headlights of oncoming or passing cars.Thus it will be appreciated that during normal daylight conditions the light detector 200 and the light detector 14 will receive substantially similar light levels and under these conditions the potentiometer 82 may be adjusted to compensate for small light level differences and circuit tollerances so that a predetermined signal which may be zero for example is provided for the amplifier 1 77.

Thus it will be readily apparent that a signal sufficient to operate the driving mirror will not be received by the amplifier 1 77 during conditions when the ambient light detected by the detector 200 is substantially the same as the light detected by the detector 14 and thus no significant output signal will under these conditions be provided on the line 214. When however the light detector 1 4 is exposed to the high light level associated with headlight glare and at the same time the ambient light detector 200 receives no such light signal, then under these conditions, a signal will be provided between the line 21 2 and the wiper 210 which will be amplified by the amplifier 1 77 so as to provide a significant signal output on the line 214 which will cause the driving mirror to operate.It will be appreciated that thc circuit as just before described with reference to Figure 10 is in effect a four arm bridge circuit wherein the light detectors 1 4 and 200 may be considered to be resistors, the resistance of which is dependant upon incident light and wherein the light detector 14 is one bridge arm, the light detector 200 is another bridge arm and the potentiometer 82 as divided by the wiper arm 210, represents the other two bridge arms.

Thus it will be quite apparent that when, due to headlight glare on the light detector 14, the bridge circuit is significantly unbalanced, the required output signal will be generated on the output line 214 to dip the driving mirror.

It is to be appreciated that the embodiments of the invention described above with reference to the drawings have been given by way of example only and that modifications may be effected. Thus, for example, the mirrors have been illustrated in the drawings as interior rear view mirrors but only minor mounting modifications are necessary for the mirrors to be exterior rear view mirrors for mounting on the wings and/or doors of motor vehicles. Furthermore, the mirrors may be produced as completely self-contained units with batteries, preferably re-chargeable batteries, as the power source.

Claims (9)

1. A rear view mirror for a motor vehicle, which rear view mirror comprises pivoting means for causing the mirror to pivot between normal and anti-glare positions in dependence upon the presence or absence of light of a predetermined intensity from a following vehicle, the pivoting means including ambient light compensation means for compensating for the affect of ambient light on the pivoting means.

2. A rear view mirror according to claim 1 in which the ambient light compensation means comprises a pair of photosensors arranged in a bridge circuit.

3. A rear view mirror according to claim 1 or claim 2 and comprising a housing having a back plate portion and a front frame portion connected to the back plate portion to define a chamber for receiving the pivoting means.

4. A rear view mirror according to claim 3 in which the mirror is pivotally mounted within the housing chamber, the lower edge of the mirror being arranged within the housing recess.

5. A rear view mirror according to any one of the preceding claims in which the pivoting means includes biasing means for biasing the mirror towards its normal position, a solenoid coil connected to the photosensors, and magnet means mounted on a rear portion of the mirror such that when light strikes the photosensors above the predetermined intensity, the solenoid coil generates a magnetic field which attracts the magnet means and causes the mirror to pivot to its anti-glare position.

6. A rear view mirror according to any one of the preceding claims and including sensitivity means for initially setting the predetermined light intensity at which the mirror is responsive.

7. A rear view mirror according to claim 6 in which the sensitivity means is a potentiometer, the potentiometer being provided with an adjustable thumb wheel.

8. A rear view mirror according to any one of the preceding claims and which is adapted to be mounted inside the motor vehicle.

9. A rear view mirror according to claim 1 and substantially as herein described with reference to the accompanying drawings.