The invention relates to a cutoff mechanism
5 for an optical module and an optical module comprising
such a cutoff mechanism. Said optical module is
particularly intended for being inserted in an
automobile projector, especially in an elliptical
projector, being arranged in the front of the
10 automobile vehicle.
Such optical modules possess a light source
that projects light on a reflector. Light is then
reflected on a lens so as to be reverted and returned
back outside the vehicle under the form of a light
15 beam. The optical modules also comprise a cutoff
mechanism enabling to block out or not a part of the
beam.
It is known to use cutoff mechanisms
comprising a rotating cutoff shield being electrically
20 operated to be moved, to order, from a first angular
position, in which it blocks out a part of the light
beam in order to limit the range of the projector to
the low beam so as not to dazzle the other drivers
circulating in the opposite direction, to a second
25 angular position, in which it does not block out the
light beam, the range of the projector then
corresponding to the high beam.
There are also so-called multifunction
projectors, in which the cutoff shield can assume more
30 than two angular positions so as to block out
selectively the light beam.
The shield is electrically operated by an
actuator comprising an electric motor. The electric
motor comprises a stator and a rotor provided with a
set of coils, also called armature windings or
armature. The armature presents a conductive wire
being wound and thus a resistance, so-called armature
5 resistance, corresponding to the resistance of the
conductive wire.
The motor is mounted on a plastic housing of
the cutoff mechanism. Due to the reduced space being
available within the optical module to position the
10 motor therein, it is known to use motors of small
sizes having a reduced volume available for the coils
and thus for the conductive wire. The conductive wire
length is thus limited. Indeed, the motor torque being
proportional to the section of the conductive wire,
15 the section cannot be reduced beyond a threshold
enabling the motor to present a sufficient torque to
operate the cutoff shield. Now, the resistance of the
conductive wire, i.e. the armature resistance being
proportional to the length of the conductive wire,
20 such "small" motor thus presents a weak armature
resistance, i.e. lower than 25 Ohms.
Consequently, for a given voltage, the
current intensity passing through the motor is
significant and the latter is thus caused to dissipate
25 much power, which leads to a significant motor selfheating.
Such self-heating phenomenon is in particular
defined by a so-called self-heating temperature.
Moreover, heat dissipated by the light
source and the sun rays entering the optical module
30 through the lens causes the internal environment of
the optical module and thus of' the motor to be heated.
Such heating phenomenon is in particular defined by a
so-called environment temperature.
The self-heating of the motor being
significant, the temperature reached by the motor,
i.e. the sum of the environment and self-heating
temperatures, is also significant, which has some
5 chance to damage the plastic housing, on which the
motor is mounted.
To remedy such disadvantage, it is known to
arrange an electronic board with the motor in the
optical module. The electronic board reduces indeed
10 the intensity of the current crossing the motor and
thus the power the motor has to dissipate. However,
such arrangement is expensive and cumbersome.
Another known solution consists in selecting
the housing in metal, in virtue of its resistance to
15 high temperatures, but such material has the
disadvantage to be heavy and expensive.
The invention thus aims at 3.mproving the
situation.
Indeed, it proposes a cutoff mechanism for
20 an optical module comprising a housing and a driving
motor provided with an armature resistance and being
arranged to cause the movement of a light beam cutoff
shield, said housing being made of a plastic material,
characterized in that said armature resistance is
25 comprised between 25 and 120 Ohms.
Thus, thanks to the increase of the motor
armature resistance beyond 25 Ohms, it is proposed to
reduce the intensity crossing the conductive wire and
thus to reduce the power the motor has to dissipate.
3 0 Thus, it is not necessary any more to arrange an
electronic board with the motor. The self-heating
temperature of the motor is then comprised between 15
and 90°C, more preferably between 30 and 50°C. In such
a way, the motor temperature stays lower than 220"~
when the light source of the optical module operates.
The motor support housing can then be selected in a
plastic material being resistant to such temperatures,
5 for example PES (Polyethylene Sulfide), PET
(Polyethylene Terephthalate) or PBT (Polybutylene
Terephthalate).
The increase of the conductive wire length
is obtained in particular thanks to an increase of the
10 motor size. Such size being limited by the maximum
space occupied by the cutoff mechanism, the section of
the conductive wire is in particular reduced so as to
increase the length thereof. The result of this is a
decrease of the motor torque. Beyond an armature
15 resistance of 120 Ohms, the motor then presents a
torque being insufficient to drive the cutoff shield
and/or a size being incompatible with the space
available within the optical module for the cutoff
mechanism.
20 In an advantageous embodiment of the
invention, said armature resistance is comprised
between 40 and 90 Ohms. In a particularly'advantageous
way, said armature resistance is substantially equal
to 55 Ohms. The term "substantially" means a tolerance
25 of more or less fifteen per cent around the target
value.
According to an advantageous embodiment of
the invention, said motor comprises at least three
coils. The motor comprises in particular three coils.
30 The presence of at least three coils in the motor
enables to provide it with a more constant torque, for
example, than a motor having two coils. The presence
of at least three coils enables to drive a motor shaft
connected to a pinion over more than half a turn, i.e.
over more than 180°, contrary to a motor only having
two coils. The presence of tree coils enables to drive
the motor shaft over more than half a turn even
5 starting from a state in which the motor shaft does
not turn yet. Thanks to the presence of three coils,
the rotation movement transmitted to the shield by the
pinion can be geared down while providing a sufficient
rotation of the shield between its first and its
10 second angular positions, i.e. a rotation of the
shield being higher than 60". Due to the gearing down,
the torque being necessary to drive the shield is less
significant, which enables to further reduce the
section of the conductive wire and thus to increase
15 the armature resistance, in particular until 120 Ohms.
According to an embodiment of the invention,
said mechanism comprises said cutoff shield.
In an interesting embodiment of the
invention, said pinion of the motor drives said cutoff
20 shield through a gear, the rotational angle of the
shield being lower than the rotational angle of said
pinion. The gear is for example an inner tooth gear.
The inner tooth gear enables to increase the space
being available for the motor within the cutoff
25 mechanism, in particular with respect to a solution
presenting an outer tooth gear. It is then possible to
select a bigger motor having a more significant
armature resistance without increasing the general
space occupied by the optical module.
3 0 Advantageously, the gearing ratio between
the pinion of the motor and the gear is comprised
between 1/5 and 1/2. It is in pa,rticular equal to 1/3.
In an embodiment of the invention, said
shield mainly extends in a first plan, said shield
having a tilted portion with respect to such first
plan in a rotation according to an axis parallel with
5 a rotational axis of the shield. The tilted portion
enables the shield to be driven with no contact with
the motor. Thus, it enables to increase the available
space for the motor within the cutoff mechanism. It is
then possible to select a bigger motor having a more
10 significant armature resistance without increasing the
general space occupied by the optical module.
According to an exemplary embodiment of the
invention, said shield is arranged to make a rotation
of at least 75" between a vertical position and a
15 tilted position.
In an embodiment of the invention, the motor
has a length higher than 26 rnm. Advantageously, the
motor has a diameter higher than 21 mrn. The increase
in the volume of the motor, i.e. of its length and/or
20 of its diameter makes it possible in particular to
increase its armature resistance.
The invention also relates to an optical
module comprising a cutoff mechanism such as above
described.
25 Other characteristics and advantages of the
invention will further appear better upon reading the
following description of an exemplary embodiment of an
optical module according to the invention, referring
to the accompanying drawing, wherein:
3 0 - Fig. 1 is a perspective schematic view of
an optical module with a cutoff mechanism;
- Fig. 2 is a perspective exploded view of
the cutting mechanism;
- Fig. 3 is perspective view of the cutoff,
mechanism illustrated on Fig. 2, once assembled;
- Fig. 4 is a schematic side view of the
motor inside and the cutoff shield according to the
5 invention; and
- Fig. 5 is a side view of the motor and the
cutoff shield according to the invention.
Fig. 1 enables to illustrate an optical
module 1 according to the invention. In such optical
10 module, there is a light source 2 generating a light
beam reflected by an optical reflector 3. The light
beam is then projected on a lens 4 that inverts it and
returns it back on the road located in the front of
the vehicle, in which the optical module is
15 positioned. The lens 4 is arranged on a lens
carrier 7. The light source is here a halogen lamp.
A cutoff mechanism 5 is arranged between the
reflector 3 and the lens 4. Such cutoff mechanism 5
enables to block out more or less the light beam in
20 reply to an order of the vehicle's user or to an
automatic order, so as to propose different lighting
modes for the road. The cutoff mechanism 5 comprises a
driving motor, in particular a direct current motor.
As illustrated on Fig. 4, the motor 30
2 5 comprises a stator 101 also called inductor and a
rotor 102. When the motor 30 operates, the stator 101
generates a magnetic field that drives into rotation
the rotor 102 around a longitudinal axis A. The
rotation movement is then transmitted to a motor
30 pinion. The motor 30 comprises for instance at least
three coils 103. It is question here of the coils 103
of the rotor 102, otherwise called armature windings
or armature. Such coils 103 comprise a conductive
wire 104, in particular in copper, and presenting a
resistance, the so-called armature resistance. The
motor 30 is thus provided with an armature resistance.
Such cutoff mechanism5 will now be
5 described more in details thanks to Figs. 2 and 3.
Further on in the description, the terms front, rear,
right, left, upper and lower are defined with respect
to the forward direction of the vehicle, i.e. with
respect to the arrow direction referenced 80 on
10 Fig. 2 .
The motor 30 is arranged so as to cause the
movement of a cutoff shield 10 for the light beam. The
motor 30 enables the shield 10 to be positioned
according to various positions, here according to two
15 positions, so as to block out more or less the light
beam. For this, the motor 30 comprises the driving
pinion 31. Such pinion 31 is connected to an inner
tooth gear 14 that drives the shield 10 in movement
and particularly in rotation, as explained further on.
20 According to the invention, the armature resistance is
comprised between 25 and 120 Ohms, in particular
between 40 and 90 Ohms and, more particularly,
substantially equa,l to 55 Ohms. Such armature
resistances are obtained in particular thanks to a
25 conductive wire of a section being substantially equal
to 0.09 mm. In the case when the motor comprises
three coils, each of them comprises for example
substantially 700 winding turns of the conductive
wire.
30 The motor operation voltage is for instance
comprised between 9 and 16 V. The power to be
dissipated by the motor is particularly comprised
between 1 and 4 Watts. The self-heating temperature of
the motor is then limited to 90°C and, in particular,
to 50"~.
The motor 30 comprises an upper side 32, a
rear side 33, a lower side 34, a front side 35, a
5 right side 36 and a left side 37. The upper side 32
and the lower side 34, being opposite to each other,
have curved shapes. They define a cylinder part, the
axis of which is located in the centre of the
motor 30, i.e. here in the centre of the pinion 31.
10 The motor 30 then takes the shape of a cylinder being
cut at the level of the front 35 and rear 33 sides.
On the right part of the motor 30 a
connection area 39 is located, being arranged so as to
connect the motor 30 with a power source, for example,
15 a current source (not shown) . Thus, the connection
area 39 defines the right side 36 of the motor 30 and
a part of the upper 32, rear 33, lower 34 and front 35
sides located on the right part of the motor 30.
The motor 30 presents a length of less than
20 35 mrn, in particular substantially equal to 30.5 mrn.
It presents a diameter of less than 30 mm, for example
substantially equal to 24.2 mm. Beyond one and/or the
other of such dimensions, the motor presents the
disadvantage to be heavy and/or expensive. With the
25 objective of reaching an armature resistance higher
than 25 Ohms, the motor has a length higher than 26 mm
and/or a diameter higher than 21 mm. The length of the
motor is measured along the axis of the motor passing
by the pinion 31 but does not contain the length of
30 the pinion. The length of the motor is then the
distance between its left side 37 and its right side
36.
The pinion 31 is located at the level of the
left side 37 of the motor 30. It is mounted on a
driving shaft 38 projecting with respect to the left
side 37 of the motor 30 and located substantially in
5 the middle of the left side 37 of the motor 30.
The cutoff mechanism 5 comprises a
housing 100, in particular in a plastic material. Such
housing 100 comprises a frame 50 of a substantially
rectangular shape so that it presents four
10 interconnected branches, so-called an upper branch 51,
a left branch 52, a lower branch 53 and a right
branch 54. The housing 100 also comprises a motor
carrier 40.
The motor 30 is mounted on the housing 100,
15 in particular at the level of the motor carrier 40.
Such motor carrier 40 is located in the centre and
towards the rear side of the frame 50, i.e. between
the motor and the light source, once the cutoff
mechanism 5 is mounted in the optical module.
20 The motor carrier 40 comprises a lower
wall 41 located opposite the lower side 34 of the
motor 30, a rear wall or bottom 42 located opposite
the rear side 33 of the motor 30, a rear part of the
upper side 32 and a rear part of the lower side 34 so
25 that the motor 30 is in contact with the rear wall 42.
The motor carrier 40 also comprises a right wall 43
with a U-shape, a central branch of the U being
arranged backwards vertically and the two side
branches of the U being substantially parallel between
30 them, horizontal and oriented forwardly . The right
wall 43 of the motor carrier 40 thus defines a notch
inside which a boss (non visible) of the connection
area 39, through which the mot'or is connected with the
current source, is inserted and makes integrally part
of the motor carrier 40. In the same way, the motor
carrier 40 comprises a left wall 44 in a U-shape, a
central branch of the U being arranged rearwards
5 vertically and the two side branches of the U being
substantially parallel between them, hprizontal and
oriented forwardly. The right wall 43 oE the motor
carrier 40 thus defines a notch inside which the
shaft 38 comprising the pinion 31 can be inserted, the
10 pinion 31 projecting then beyond the carrier 40 of the
motor 30 towards the left.
The cutoff mechanism 5 also comprises a
thermal screen 60 meeting an external side of the rear
wall 42 of the carrier 40 of the motor 30, i.e. a side
15 oriented rearwards. The heat screen 60 is thus located
between the motor carrier 40 and the light source. It
is made of a metal so that it protects the motor
carrier 40 and the motor 30 from heat dissipated by
the light source.
20 The cutoff shield 10 is part of the cutoff
mechanism 5. It is arranged so as to block out more or
less the light beam, i.e. to cut more or less the
light beam. The shield mainly extends along a first
plan. The shield 10 can be positioned here according
25 two positions, a first position in which it blocks out
partially the light beam and corresponding to the low
beam, and a second position in which it does not block
out the light beam and corresponding to the high beam.
In the first position thereof, the cutoff shield 10
30 extends according to a substantially vertical plan,
whereas, in the second position thereof, it extends in
a substantially horizontal plan, for example being
substantially tilted of 75" with respect to the
vertical. It is here a bi-functional cutoff
mechanism 5.
The cutoff shield 10 is positioned opposite
the light source. It is mounted on a shield carrier 11
5 comprising a first part 12 provided with the inner
tooth gear 14, located at the level of a first
longitudinal end of the shield 10, and a second part
13 provided with a return spring 15 tending to bring
the shield back in its first position, i.e. in its
10 substantially vertical position, the second part 13
being located at the level of a second longitudinal
end of the shield 10. The cutoff shield 10 is made of
steel so as to resist the strong heats emitted by the
light source, whereas the first part 12 and the second
15 part 13 of the shield carrier 11 are in plastics,
because they are off-centre with respect to the light
source and thus less exposed than the shield 10 to the
heat emitted by the light source. The spring 15 of the
second part 13 is however in metal. The first
20 longitudinal end is located on the left part of the
shield 10, whereas the second longitudinal end is
located on the right part of the shield 10.
The second part 13 comprises a clip 21
pinching the shield through the bottom and on either
25 side of the latter, i.e. it pinches it on a front side
and on a rear side of the shield 10 so as to support
it. The clip 21 of the second part 13 originates at
the level of an arm 22, that the second part 13
comprises, extending parallel to a longitudinal
30 extension axis of the shield 10. At the level of a
distal end of the arm 22 located on the right part
there is an excrescence 23 extending beyond the shield
10 towards the right. The spring 15 is here wound
around the arm 22 of the second part 13 and exerts a
return force on the clip 21 of the second part 13.
The first part 12 of the shield carrier 11
comprises a central body 16 of a substantially
5 parallelepiped shape from which a clip 17 originates
to pinch the shield 10 from the bottom so as to
support it. The clip 17 of the first part 12 is
similar to the clip of the second part 13, i.e. it
pinches the shield 10 on the front side and on the
10 rear side of the latter. The first part 12 of the
carrier 11 also comprises an excrescence 18 projecting
with respect to the central body 16, towards the left
part and extending beyond the shield 10 towards the
left part.
15 From the central body 16 two arms also
originate, so-called first and second arms 19, 20. The
first arm 19 extends in a common plan with the
shield 10, perpendicular to the longitudinal extension
direction of the shield 10. The second arm extends
20 according to a direction perpendicular to the plan in
which the shield 10 extends, i.e. perpendicular to the
first arm 19. The inner tooth gear 14 connects the
first arm 19 with the second arm 20 and has a
substantially circular shape so that it forms a
25 quadrant between the first and the second arms 19, 20.
The gearing ratio between the pinion 31 of
the motor 30 and the gear 14 is here equal to 1/3. The
presence of at least three coils enables to drive the
pinion on more than 180" around its axis of rotation,
3 0 so as to drive the cutoff shield on more than 60"
around its axis of rotation when the gear ratio is
1/3. With a rotation of 3 6 0 ° , the pinion will be able
to drive the cutoff shield in a rotation of 120". The
gear ratio could of course be different, according to
the motor torque and/or the desired rotation of the
shield. It will be comprised in particular between 1/5
and 1/2.
5 The fact that the gear 14 is provided with
inner teeth enables the motor 30 to move back with
respect to the frame 50 and thus to reduce the space
occupied by the mechanism cutoff 5 while keeping a
gearing ratio of 1/3 necessary for the rotation
10 driving of the shield 10.
The shield carrier 11 is mounted on the
frame 50. On the right branch 54 of the frame 50 a
groove is arranged, having a flared shape towards the
front part and presenting an opening 56 at the level
15 of a rear end, arranged to receive the excrescence 23
of the second part 13 of the carrier. The
excrescence 23 of the second part of the shield
carrier 11 is thus inserted into the groove 55 from
the front to the rear up to the moment where it enters
20 the opening 56. On a same way, on the left branch 52
of the frame 50 there is a groove 57 of a similar
shape as the groove of the right branch 54, i.e. with
a flared shape towards the front and having an
opening (non visible) at the level of a rear end
25 arranged to receive the excrescence 18 of the first
part 12 of the carrier.
Moreover, the frame 50 comprises borings
being distributed on the branches 51, 52, 53, 54
thereof and arranged to mount the cutoff mechanism 5
30 in the optical module.
It should be noticed here that the shield 10
comprises a rotation axis defined by the
excrescences 18, 23. Such rotation axis is offset with
respect to the rotation axis of the motor 30, i.e. the
rotation axis of the pinion 31. The rotation axis of
the shield 30 is located in particular above the motor
rotation axis along a vertical axis.
5 Figs. 4 and 5 allow a particularly
advantageous embodiment of .the invention to be
illustrated, according to which the shield presents a
tilted portion 71. Fig. 4 illustrates the shield 10 in
its first position, i.e. in its vertical position. The
10 vertical position corresponds to the position in which
the cutoff shield blocks out the light beam so as to
limit the range of the projector to the low beam.
Fig. 5 represents the shield 10 in its second
position, i,e.' in its tilted position of substantially
15 75" with respect to the vertical. The tilted position
gorresponds to the position in which it does not block
out or almost not the light beam, the range of the
projector then corresponding to the high beam.
The tilted portion 71 iq located on a
20 central area of the shield 10. The central area is
here located above the motor 30. The tilted portion 71
occupies a lower band of the shield 10, i.e. a band
being close to the motor 30. It is tilted towards the
back of the cutoff mechanism. It is tilted according
25 to an axis of rotation parallel with the axis of
rotation of the shield. The shield 10 also comprises a
plane wall 72 extending in the first plan. The plane
wall 72 is here located above the tilted wall 71.
Parts of the plane wall 72, so-called first and second
3 0 tabs 73 extend on either part of the tilted wall 71,
i.e. on each longitudinal end side of the tilted
wall 71. Fins 74 connect the longitudinal ends of the
tilted wall 71 with the tabs 73. The tabs 73 are
located on either part of the motor 30, i.e. beyond
the left and right sides of the motor 30. When the
shield 10 modifies its position, the tabs 73 thus do
not come into contact with the motor 30.
The tilted portion 71 of the shield 10
allows, when the shield is in its vertical position,
the light beam to be sufficiently blocked out so as to
enable the projector to light the road with low beam.
It enables the shield to carry out a rotation movement
of substantially 75" around its rotation axis without
coming into contact with the motor. Such rotation
allows the shield 10 to reach its second position and
to let the light beam free so as to allow the
projector to light the road with high beam. This slope
thus makes it possible to release some space for the
motor, whatever the position of the shield.
It is mainly thanks to the inner tooth
gearing and/or to the shape of the shield, i.e. thanks
to the tilted portion, that it is possible to arrange
a motor of greater size within the housing without
modifying the space occupied by the optical module.

CLAIMS
1. A cutoff mechanism (5) for an optical module
comprising a housing (100) and a driving
5 motor (30) provided with an armature resistance
and being arranged to cause the movement of a
light beam cutoff shield (10), said housing (100)
being made of a plastic material, characterized in
that said armature resistance is comprised between
10 2 5 and 120 Ohms.
2. The cutoff mechanism (5) according to claim 1,
wherein said armature resistance is comprised
between 40 and 90 Ohms.
3. The cutoff mechanism (5) according to claim 1 or
15 2, wherein said armature resistance is
substantially equal to 55 Ohms.
4. The cutoff mechanism (5) according to any of
claims 1 to 3, wherein said motor (30) comprises
at least three coils.
20 5. The cutoff mechanism (5) according to any of
claims 1 to 4, wherein said mechanism (5)
comprises said cutoff shield.
6. The cutoff mechanism (5) according to claim 5,
wherein a pinion (31) of the motor (30) drives
25 said cutoff shield (5) through a gear (14), the
rotational angle of the shield being lower than
the rotational angle of said pinion.
7. The cutoff mechanism (5) according to claim 6,
wherein the gearing ratio between the pinion (31)
30 of the motor (30) and the gear is comprised
between 1/5 and 1/2.
8. The cutoff mechanism (5) according to any of
claims 5 to 7, wherein said shield (10) mainly
18
extends in a first plan, said shield (10) having a
tilted portion (71) with respect to such first
plan in a rotation according to an axis parallel
with, a rotational axis of the shield.
5 9. The cutoff mechanism (5) according to any of
claims 5 to 8, wherein, said shield (10) is
arranged to make a rotation of at least 75°
between a vertical position and a tilted position.
10. The cutoff mechanism (5) according to any of
10 claims 1 to 9, wherein the motor has a length
higher than 26 mm.
11. The cutoff mechanism (5) according to any of
claims 1 to 10, wherein the motor has a diameter
higher than 21 ram.
15 12. An optical module (1) characterized in that it comprises a cutoff mechanism (5) according to any of claims 1 to 11.