Rear view mirror

A motor vehicle rear view mirror is disclosed having a mirror glass which pivots automatically from a normal position to an anti-glare position in response to headlight glare. The glass is mounted between a front frame and a back plate of a two part housing and carries a magnetic member for co-operating with a solenoid coil of an electrical assembly. The electrical assembly is formed as a single unit mounted in the back plate and includes a photosensor receiving light through a partly silvered region of the mirror glass. A signal from the photosensor is amplified by one or more transistors to energize the solenoid coil. A pair of switch contacts is actuated when the mirror glass changes its position to the anti-glare position and is arranged to reduce current flow in the coil to a level just sufficient to hold the mirror glass in the anti-glare position. The rear of the mirror housing is coupled to a mounting arm by a ball and socket joint, the socket comprising an elongate bore having an inwardly tapering section to receive balls of various diameters. A locking member is secured in the bore in order to retain the ball in the bore.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
This invention relates to a rear view mirror for a motor vehicle, which is 
movable automatically between a normal viewing position and an anti-glare 
position in which glare from light reflected from the mirror is reduced. 
(2) Description of the Prior Art 
Automatically adjusting rear view mirrors are known as shown by the 
following patents in which such mirrors have been proposed. 
U.S. Pat. No. 3,152,216 to M. L. Woodward 
W. German Offenlegungsschrift No. 2 133 182 to G. Paul 
British Pat. No. 1 346 483 to K. A. Grell 
French Pat. No. 1 463 007 to Chipoff et Perrier U.S. Pat. No. 3,152,216 
discloses an automobile rear view mirror comprising a housing that 
receives a mirror glass and an arrangement which automatically pivots the 
mirror from its normal viewing position to an anti-glare position in 
response to headlights of a following car shining into the mirror. The 
mirror glass has an unsilvered portion to which is attached a 
photodetector for detecting light incident on the mirror. The assembly of 
the photodetector and the mirror glass is mounted on a metal plate which 
is pivotally mounted on a bracket centrally of the mirror glass, the 
bracket being mounted in the housing. The bracket also carries an 
electrical circuit including a thermionic valve responsive to the 
photodetector and which drives a relay to operate in response to a 
predetermined light level incident on the photodetector. The relay is 
arranged to switch electric current to a solenoid coil in such a manner 
that the coil attracts the metal plate and thereby pivots the mirror to 
its anti-glare position. 
A disadvantage of this prior art mirror is that it is relatively complex 
and expensive to produce particularly because the photodetector has to be 
mounted separately from the rest of the circuitry on a separate bracket on 
the mirror, and also because metal pivot joints and a metal bracket are 
required to pivotally mount the mirror in the housing. Also, the valve 
driven circuitry is relatively bulky and is relatively insensitive to 
incident light due to the fact that it requires a relay to switch current 
to the solenoid coil. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an improved 
automatically adjusting rear view mirror for a motor vehicle which is of a 
less complicated construction and is relatively inexpensive to produce. 
It is another object of the invention to provide an automatically adjusting 
rear rear mirror having a more sensitive electrical circuit which is of a 
simpler physical construction. 
It is a further object of the invention to provide a rear view mirror with 
a simpler pivotal mounting of the mirror glass. 
The present invention provides a rear view mirror for a motor vehicle, 
including a housing in which a mirror glass is pivotally mounted for 
movement between a normal viewing position and an anti-glare position in 
which glare from light reflected from the mirror is reduced, a solenoid 
coil for moving the mirror glass to the anti-glare position, and a 
photosensor for responding to light incident on the mirror, wherein in 
accordance with one aspect of the invention, the photosensor, associated 
drive circuitry and the solenoid are formed as a single unit on a circuit 
board. The formation of this electrical assembly as a single unit provides 
for a very significant cost advantage during assembly of the mirror 
because the electrical components of the mirror can be dropped into and 
secured in the mirror housing as a simple operation during assembly of the 
mirror. 
In accordance with another aspect of the invention, the mirror housing 
consists of a back plate part and a front frame which co-operate to define 
a pivotal mounting for the mirror glass. The mirror glass is received 
between these two housing parts such that the glass is pivotally mounted 
at one of its edges by the housing parts. This arrangement simplifies the 
structure and manufacturing steps required to assemble the mirror. After 
installation of the electrical assembly in the back plate part of the 
housing, the mirror glass is dropped into the back plate part, and the 
front frame is installed, overcoming the requirement for the metal 
brackets and the metal pivot joints of the prior art aforesaid. 
In accordance with another aspect of the invention, the electrical assembly 
includes a circuit arrangement which comprises means to receive an 
electrical supply from the vehicle and to connect the supply to the 
photosensor, means responsive to the supply and arranged to establish a 
reference voltage, an operational amplifier arranged to compare the output 
voltage with the reference voltage, and a transistor responsive to the 
output of the operational amplifier for controlling the flow of electrical 
current through the solenoid coil. This circuit arrangement has the 
advantage of overcoming the requirement of the relay of the prior art and 
provides for a more sensitive circuit. The circuit arrangement also has 
the advantage that together with the photosensor it can be arranged to be 
sensitive to tungsten light but not to sodium light which provides for 
discrimination against light from street lamps. 
Other features, objects and advantages of the invention will appear from 
the following description of preferred embodiments thereof given by way of 
illustrative example with reference to the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring to FIGS. 1 to 4 there is shown a rear view mirror comprising a 
housing 2 formed as a synthetic plastic molding in two parts, namely a 
back plate part 4 and a front frame part 6. Located between the two parts 
of the housing is a mirror glass 8 movable between a normal viewing 
position (FIG. 2) and an anti-glare position (FIG. 3) in which glare from 
light reflected from the mirror is reduced. The mirror is pivotable about 
a pivot 10. An electrical assembly also includes a solenoid coil 16 which 
is energized in response to light incident upon the mirror above a 
predetermined intensity, the coil co-acting with a magnetic member 18 
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 to the construction of the housing, back plate 
4 is in the form of a tray with rear walls 30 (FIG. 4) tapering to provide 
a deepened portion at the center 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 the electrical assembly 12. The rear of 
the back plate provides a socket 36 of a ball and socket joint which 
serves to receive a ball member 38 of mounting arm 22. Mounting arm 22 is 
thus held mounted to 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. 
Referring to the construction of socket 36 as shown in FIG. 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 installed 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 by 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 extend into the interior of 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 back plate member 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 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 provided 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 FIG. 5) to a potentiometer in the form of a 
thumb-wheel 82 which regulates the sensitivity of the electrical assembly, 
i.e. the thumb-wheel 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 112. The collector circuit of transistor 112 includes 
solenoid coil 16. A protection 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 FIGS. 2 and 3. 
As can be seen in FIGS. 2 and 3 the physical disposition of the electrical 
assembly is such that the core of the solenoid 16 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 120 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 18 and a tine 124 of an upstanding member 126. The edge 128 of 
member 126 remote from board 104 has a recess 130 to receive tine 122 
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 as at 142 in order to provide a buffer when mirror glass 
8 moves to the anti-glare position. 
In operation of the rear view mirror 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 18 and to thus move 
mirror glass 8 about pivot 10 to the anti-glare position (FIG. 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 116 are closed which has the effect of shorting out 
part of coil 16 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 FIG. 6, parts 
similar to those of FIG. 5 are indicated by similar reference numerals. 
Transistor 112 serves to amplify the current generated in resistor 108 and 
a main switching transistor 150 is coupled to the collector circuit of 
transistor 110 via resistors 152, 154 and diode 156. Coil 16 is connected 
in the collector circuit of transistor 150 together with a series resistor 
158. Contacts 116 which are closed in the normal position of mirror glass 
8 are connected across resistor 158. 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 116 are opened so that resistor 158 is 
switched into coil 16 in order to reduce current flow through coil 16 and 
provide a holding current. 
Another embodiment of a rear view mirror according to the invention is 
shown in FIGS. 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 FIGS. 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 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 160 integrally moulded in the back 
plate part 4. 
An electrical assembly 12 is mounted in the housing 2 on studs 34 at the 
back of the part 4, as by gluing. The electrical assembly 12 is formed as 
a single unit wherein all of the electrical components of the mirror are 
mounted on a single circuit board 161. As with the previously described 
embodiment, the electrical assembly 12 includes a photosensor 14 which 
receives light incident on the mirror glass 8 through an aperture 162 
formed in the silvered layer 163 of the mirror glass, the assembly 12 
further including 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 16 which co-operates with a metal plate 164 carried by the 
mirror to pivot the mirror to its anti-glare position. 
The coil 16 of the FIGS. 8 and 9 embodiment differs from that of the FIGS. 
1 to 4 embodiment in that its axis is arranged generally parallel to the 
plate of the circuit board 161, the coil having generally L-shaped pole 
pieces 165, 166 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 181 which receives a 
ball 182 of a mounting arm 167. 
The circuit included on the printed circuit board 161 is shown in detail in 
FIG. 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 against 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, 169 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, 
169 in a potentiometer chain including resistors 173 to 175, whereby the 
potential at point 176 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 
177 connected as a comparator. The output of the operational amplifier 177 
is connected to a zener diode 178 and hence to the base of a control 
transistor 179 which controls the current flowing in the solenoid coil 16. 
A resistor 180 provides a current path for both the base leakage current 
of the transistor 179 and the leakage current of the diode 178. 
In use, when increased illumination causes the potential at point 176 to 
exceed the reference voltage set by the potentiometer 82, the output of 
the amplifier 177 goes high. When the output exceeds the threshold set by 
the zener diode 178, the transistor 179 is switched on, energizing the 
coil 16 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 virture of the unitary nature of the 
electrical assembly 12 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 12 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 cost.